add Catppuccin Mocha theme (+ high-contrast sibling)

Ships catppuccin-mocha (faithful to the official Catppuccin Mocha
palette) and catppuccin-mocha-hc (high-contrast sibling per D-69 — the
faithful palette is never retuned to pass the gate). Both bundled and
gated: mocha clears baseline AA, mocha-hc clears the strict extended
set. Catppuccin MIT palette recorded in licenses.yaml.

Closes T-82 (Mocha + hc meets every acceptance bullet; faithful Latte
deferred — it can't clear baseline AA without retuning, a separate call).

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

lib/main.dart

@@ -425,6 +425,8 @@ Future<List<ThemeDefinition>> _loadBundledThemes() async {
     '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) {