refactor(settings): ClideSettings — one live-preferences facade (D-101)

Introduce ClideSettings, a single widget-facing facade for the app's live
user preferences, namespaced by concern: ClideSettings.fonts.monoOf(context)
/ .fonts.uiOf(context), ClideSettings.theme.of(context),
ClideSettings.i18n.of(context). "Plumb once, use many."

Fonts are carried by a new root-provided ClideSettingsScope (resolved from the
font settings in root_shell, rebuilt on change); theme and i18n delegate to
their existing live providers (ClideTheme / the I18n service) so there's one
source of truth and their many consumers migrate incrementally rather than in
a big-bang. Reads outside a scope fall back to the bundled font defaults, so a
widget renders without a provider (isolated tests).

Migrate ~93 monospace-font call sites across 33 files from the clideMonoFamily
const to ClideSettings.fonts.monoOf(context) — pure refactor, identical family
when no override is set. 11 context-less helper sites (markdown static spans,
a few top-level/static builders) keep the const for now and are tracked in
T-472. Records D-101; updates the ui-design skill's font-family rule.

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

lib/builtin/settings_ui/src/settings_category_view.dart

@@ -128,7 +128,12 @@ class _SectionCard extends StatelessWidget {
           if (section.label.isNotEmpty)
             Padding(
               padding: const EdgeInsets.only(left: 2, bottom: 6),
-              child: ClideText(section.label.toUpperCase(), fontSize: clideFontCaption, color: tokens.sidebarSectionHeader, fontFamily: clideMonoFamily),
+              child: ClideText(
+                section.label.toUpperCase(),
+                fontSize: clideFontCaption,
+                color: tokens.sidebarSectionHeader,
+                fontFamily: ClideSettings.fonts.monoOf(context),
+              ),
             ),
           ClideSurface(
             // Card surface (surface.md): panelHeader resolves to the `surface`
@@ -440,7 +445,7 @@ class _EditControlState extends State<_EditControl> {
         child: EditableText(
           controller: _controller,
           focusNode: _focus,
-          style: TextStyle(fontFamily: clideMonoFamily, fontSize: clideFontMono, color: tokens.globalForeground),
+          style: TextStyle(fontFamily: ClideSettings.fonts.monoOf(context), fontSize: clideFontMono, color: tokens.globalForeground),
           cursorColor: tokens.globalFocus,
           backgroundCursorColor: tokens.globalTextMuted,
           maxLines: 1,

lib/builtin/settings_ui/src/settings_modal.dart

@@ -202,7 +202,7 @@ class _CategoryRail extends StatelessWidget {
                 i.string('rail.header', namespace: SettingsModal.ns, placeholder: 'Categories'),
                 fontSize: clideFontCaption,
                 color: tokens.sidebarSectionHeader,
-                fontFamily: clideMonoFamily,
+                fontFamily: ClideSettings.fonts.monoOf(context),
               ),
             ),
             Expanded(