feat(theme): canonical theme/namespace lists + ship Summer Night (T-371, T-478)

The bundled-theme list and the Tier-0 i18n namespace list were each
hand-maintained in 3+ places that had drifted: the testmode harness loaded
8 themes (catppuccin silently unvalidated) while the app and contrast gate
loaded 10, and the i18n gate checked 4 of the shipped namespaces. Export
one canonical const each — kBundledThemePaths and kTier0Namespaces — and
have the app, the testmode harness, and the a11y gates iterate them.

Drift-proof meta-assertions:
- contrast gate fails if any theme YAML on disk is absent from
  kBundledThemePaths (so a theme can't sit unvalidated).
- i18n gate derives its subjects from assets/i18n/en_us/ at test time and
  asserts en/nl key parity for every shipped catalog (26, was 4), plus that
  every kTier0Namespaces entry has a shipped catalog.

Surfaced summer-night.yaml: a legacy-ported palette on disk, unbundled and
never contrast-checked. Per the maintainer's call, ship it: flesh the
palette to full token + syntax coverage (honouring the v1.2 colours, clide
derivation pattern for the new keys) and add a structurally identical
summer-night-hc sibling that clears the strict extended gate. Both pass.

No licenses.yaml change: summer-night is clide's own (ported from legacy
clide v1.2 under legacy/, MIT); the only third-party palette, Catppuccin,
is already acknowledged; no fonts added.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/kernel/kernel.dart

@@ -45,6 +45,7 @@ export 'src/focus.dart';
 export 'src/i18n/catalog_loader.dart';
 export 'src/i18n/fallback_chain.dart';
 export 'src/i18n/i18n.dart';
+export 'src/i18n/tier0_namespaces.dart';
 export 'src/net.dart';
 export 'src/notify.dart';
 export 'src/os.dart';
@@ -63,6 +64,7 @@ export 'src/panels/layout_preset.dart';
 export 'src/panels/registry.dart';
 export 'src/panels/slot_id.dart';
 export 'src/panels/view_pane_snapshot.dart';
+export 'src/theme/bundled_themes.dart';
 export 'src/theme/contrast.dart';
 export 'src/theme/controller.dart';
 export 'src/theme/loader.dart';

lib/kernel/src/i18n/tier0_namespaces.dart

@@ -0,0 +1,25 @@
+/// Canonical list of Tier-0 i18n namespaces preloaded at boot — the single
+/// source of truth (T-371).
+///
+/// `lib/main.dart` preloads exactly these (framework chrome under `core`, plus
+/// the catalogs of the built-ins that activate at Tier 0); the i18n coverage
+/// gate validates every one of them. The other ~17 catalogs that ship belong
+/// to built-ins that activate lazily in later tiers — their catalogs load on
+/// activation, and the gate validates them through the assets-dir sweep rather
+/// than this preload list.
+library;
+
+/// Namespaces whose catalogs are loaded at boot, before any extension that
+/// owns them has activated. `core` holds framework chrome that lives outside
+/// any extension (lib/widgets, lib/kernel, shared reader chrome — T-469).
+const List<String> kTier0Namespaces = [
+  'core',
+  'builtin.default-layout',
+  'builtin.welcome',
+  'builtin.ipc-status',
+  'builtin.theme-picker',
+  'builtin.terminal',
+  'builtin.files',
+  'builtin.claude',
+  'builtin.editor',
+];

lib/kernel/src/theme/bundled_themes.dart

@@ -0,0 +1,38 @@
+/// Canonical list of the bundled theme asset paths — the single source of
+/// truth for which themes ship (T-371).
+///
+/// Three consumers used to hand-maintain their own copy and drifted apart
+/// (main.dart loaded 10, the testmode harness loaded 8 — catppuccin was
+/// silently unvalidated, and the WCAG contrast gate had a third copy):
+///
+/// - `lib/main.dart` `_loadBundledThemes()` — what the running app loads.
+/// - `lib/test_app.dart` — the testmode platform-integration harness.
+/// - `test/a11y/contrast_test.dart` — the WCAG-AA contrast gate.
+///
+/// They now all iterate this list, so adding a theme here loads it, validates
+/// it, and ships it everywhere at once. The contrast gate additionally asserts
+/// every `.yaml` under [kThemesDir] is in this list, so a new theme cannot sit
+/// on disk (or ship) unvalidated.
+library;
+
+/// Directory holding the theme YAML sources, relative to the repo root.
+const String kThemesDir = 'lib/kernel/src/theme/themes';
+
+/// Theme YAML asset paths bundled into the app, in display order: the base
+/// themes, then their `-hc` high-contrast siblings, then third-party / ported
+/// palettes paired with their own `-hc` siblings. Every base theme has a
+/// structurally identical `-hc` sibling that clears the strict contrast gate.
+const List<String> kBundledThemePaths = [
+  '$kThemesDir/clide.yaml',
+  '$kThemesDir/midnight.yaml',
+  '$kThemesDir/paper.yaml',
+  '$kThemesDir/terminal.yaml',
+  '$kThemesDir/clide-hc.yaml',
+  '$kThemesDir/midnight-hc.yaml',
+  '$kThemesDir/paper-hc.yaml',
+  '$kThemesDir/terminal-hc.yaml',
+  '$kThemesDir/catppuccin-mocha.yaml',
+  '$kThemesDir/catppuccin-mocha-hc.yaml',
+  '$kThemesDir/summer-night.yaml',
+  '$kThemesDir/summer-night-hc.yaml',
+];

lib/kernel/src/theme/themes/summer-night-hc.yaml

@@ -0,0 +1,44 @@
+# summer-night-hc — high-contrast sibling of `summer-night`.
+#
+# Same cyan/teal/pink silhouette and identical schema; muted text, status
+# chips, syntax tokens, and the focus border are brightened to clear the
+# strict contrast gate (D-22 + D-69, `extendedPairs` in
+# lib/kernel/src/theme/contrast.dart). Backgrounds/surface/foreground are
+# unchanged from the base so the two read as the same theme.
+
+name: summer-night-hc
+display_name: Summer Night (high contrast)
+dark: true
+
+palette:
+  primary: "#5cc8ec"
+  secondary: "#5fd6cb"
+  accent: "#ff84a6"
+
+  background: "#21262f"
+  surface: "#393e48"
+  panel: "#292e38"
+
+  foreground: "#e2e8f5"
+  muted: "#c4cad6"
+
+  success: "#3fd6c0"
+  warning: "#e6b072"
+  error: "#ff9b99"
+  info: "#6cc8ec"
+
+  surfaceHi: "#434a57"
+  border: "#3a414d"
+  borderHi: "#5cc8ec"
+  textDim: "#c4cad6"
+  textMute: "#9aa2b2"
+  accentSoft: "#21ff84a6"
+
+syntax:
+  keyword: "#ffa0c0"   # pink
+  type: "#6cd4f0"      # cyan
+  string: "#9fe0c0"    # green
+  number: "#f0c888"    # amber
+  comment: "#9aa2b2"   # muted
+  method: "#80d0e8"    # teal-cyan
+  punct: "#c4cad6"     # dim

lib/kernel/src/theme/themes/summer-night.yaml

@@ -1,24 +1,27 @@
-# Summer Night — ported from legacy clide v1.2.0.
-# Palette-only; the three-tier resolver fills semantic + surface from
-# defaults. Override sections land here as the token surface grows.
+# Summer Night — cyan/teal/pink on blue-grey (ported from legacy clide v1.2.0).
+#
+# The 12 original palette colors are kept as the v1.2 designer chose them. The
+# expanded keys (surfaceHi, border/borderHi, textDim/textMute, accentSoft) and
+# the syntax set follow the clide derivation pattern, re-tinted to this theme's
+# identity. Base honours the design and clears the canonical contrast gate;
+# the high-contrast sibling (summer-night-hc) clears the strict extended gate.
 
 name: summer-night
 display_name: Summer Night
 dark: true
 
 palette:
-  # Accents (legacy names: primary/secondary/accent)
-  primary: "#00a3d2"      # cyan
-  secondary: "#00a9b9"    # teal
-  accent: "#fa5f8b"       # pink
+  # Accents (legacy: primary cyan / secondary teal / accent pink)
+  primary: "#00a3d2"
+  secondary: "#00a9b9"
+  accent: "#fa5f8b"
 
   # Backgrounds
   background: "#21262f"
   surface: "#393e48"
   panel: "#292e38"
 
-  # Text. `muted` is WCAG-AA-calibrated against `panel` — don't darken
-  # without re-running the a11y/contrast suite.
+  # Text. `muted` is WCAG-AA-calibrated against `panel`.
   foreground: "#e2e8f5"
   muted: "#a6adbb"
 
@@ -27,3 +30,20 @@ palette:
   warning: "#d08447"
   error: "#f06c6f"
   info: "#00a3d2"
+
+  # Expanded keys (clide pattern, summer-night tint)
+  surfaceHi: "#434a57"
+  border: "#3a414d"
+  borderHi: "#4a5260"
+  textDim: "#9aa2b2"
+  textMute: "#727a8a"
+  accentSoft: "#21fa5f8b"
+
+syntax:
+  keyword: "#fa8fb0"   # pink
+  type: "#5ec8e6"      # cyan
+  string: "#7fd3a8"    # green
+  number: "#e0b070"    # amber
+  comment: "#727a8a"   # muted
+  method: "#6fc6e0"    # teal-cyan
+  punct: "#9aa2b2"     # dim

lib/main.dart

@@ -393,7 +393,7 @@ Future<void> main() async {
     appDir: appDir,
     bundledThemes: themes,
     i18nLoader: AssetCatalogLoader(bundle: rootBundle),
-    preloadNamespaces: _tier0Namespaces,
+    preloadNamespaces: kTier0Namespaces,
     // Languages the UI can switch to (Settings → Appearance, T-462). Each needs
     // an assets/i18n/<locale>/ catalog folder; root_shell applies the persisted
     // app.locale on boot.
@@ -537,39 +537,13 @@ Future<Directory> _resolveAppDir() async {
 
 Future<List<ThemeDefinition>> _loadBundledThemes() async {
   const loader = ThemeLoader();
-  const paths = [
-    'lib/kernel/src/theme/themes/clide.yaml',
-    'lib/kernel/src/theme/themes/midnight.yaml',
-    'lib/kernel/src/theme/themes/paper.yaml',
-    'lib/kernel/src/theme/themes/terminal.yaml',
-    'lib/kernel/src/theme/themes/clide-hc.yaml',
-    'lib/kernel/src/theme/themes/midnight-hc.yaml',
-    'lib/kernel/src/theme/themes/paper-hc.yaml',
-    'lib/kernel/src/theme/themes/terminal-hc.yaml',
-    'lib/kernel/src/theme/themes/catppuccin-mocha.yaml',
-    'lib/kernel/src/theme/themes/catppuccin-mocha-hc.yaml',
-  ];
   final out = <ThemeDefinition>[];
-  for (final p in paths) {
+  for (final p in kBundledThemePaths) {
     out.add(await loader.fromAsset(rootBundle, p));
   }
   return out;
 }
 
-/// Every Tier-0 extension that ships an i18n catalog. Extensions
-/// registered but not active (the 17 stubs) don't preload — their
-/// catalogs load lazily on activate in later tiers.
-
-const List<String> _tier0Namespaces = [
-  // Framework chrome that lives outside any extension (lib/widgets, lib/kernel,
-  // shared reader chrome) resolves under the 'core' namespace (T-469).
-  'core',
-  'builtin.default-layout',
-  'builtin.welcome',
-  'builtin.ipc-status',
-  'builtin.theme-picker',
-  'builtin.terminal',
-  'builtin.files',
-  'builtin.claude',
-  'builtin.editor',
-];
+// The Tier-0 i18n namespace list now lives in
+// lib/kernel/src/i18n/tier0_namespaces.dart as `kTier0Namespaces`, the single
+// source of truth shared with the i18n coverage gate (T-371).

lib/test_app.dart

@@ -247,17 +247,7 @@ class _ClideTestAppState extends State<ClideTestApp> {
     // Theme loading
     try {
       const loader = ThemeLoader();
-      const paths = [
-        'lib/kernel/src/theme/themes/clide.yaml',
-        'lib/kernel/src/theme/themes/midnight.yaml',
-        'lib/kernel/src/theme/themes/paper.yaml',
-        'lib/kernel/src/theme/themes/terminal.yaml',
-        'lib/kernel/src/theme/themes/clide-hc.yaml',
-        'lib/kernel/src/theme/themes/midnight-hc.yaml',
-        'lib/kernel/src/theme/themes/paper-hc.yaml',
-        'lib/kernel/src/theme/themes/terminal-hc.yaml',
-      ];
-      for (final p in paths) {
+      for (final p in kBundledThemePaths) {
         final name = p.split('/').last.replaceAll('.yaml', '');
         try {
           final theme = await loader.fromAsset(rootBundle, p);
@@ -277,7 +267,7 @@ class _ClideTestAppState extends State<ClideTestApp> {
       final themes = <ThemeDefinition>[];
       try {
         const loader = ThemeLoader();
-        themes.add(await loader.fromAsset(rootBundle, 'lib/kernel/src/theme/themes/clide.yaml'));
+        themes.add(await loader.fromAsset(rootBundle, kBundledThemePaths.first));
       } catch (_) {}
 
       final services = await KernelServices.boot(