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/menubar/src/about_dialog.dart

@@ -67,7 +67,7 @@ class _Kv extends StatelessWidget {
         children: [
           SizedBox(width: 90, child: ClideText(label, fontSize: 13, color: tokens.globalTextMuted)),
           Expanded(
-            child: ClideText(value, fontSize: 13, fontFamily: clideMonoFamily, maxLines: 1, overflow: TextOverflow.ellipsis),
+            child: ClideText(value, fontSize: 13, fontFamily: ClideSettings.fonts.monoOf(context), maxLines: 1, overflow: TextOverflow.ellipsis),
           ),
         ],
       ),
@@ -106,7 +106,7 @@ class _Licenses extends StatelessWidget {
                 child: ClideText(
                   '${d.name} ${d.version} · ${d.license}',
                   fontSize: 12,
-                  fontFamily: clideMonoFamily,
+                  fontFamily: ClideSettings.fonts.monoOf(context),
                   color: tokens.globalTextMuted,
                   maxLines: 1,
                   overflow: TextOverflow.ellipsis,

lib/builtin/menubar/src/file_actions.dart

@@ -137,7 +137,12 @@ class _OpenFolderDialogState extends State<OpenFolderDialog> {
             child: EditableText(
               controller: _controller,
               focusNode: _focus,
-              style: TextStyle(color: tokens.globalForeground, fontSize: 14, fontFamily: clideMonoFamily, fontFamilyFallback: clideMonoFamilyFallback),
+              style: TextStyle(
+                color: tokens.globalForeground,
+                fontSize: 14,
+                fontFamily: ClideSettings.fonts.monoOf(context),
+                fontFamilyFallback: clideMonoFamilyFallback,
+              ),
               cursorColor: tokens.globalForeground,
               backgroundCursorColor: tokens.globalTextMuted,
               onSubmitted: (_) => unawaited(_submit()),

lib/builtin/menubar/src/menu_bar.dart

@@ -162,7 +162,12 @@ class _TopMenuButtonState extends State<_TopMenuButton> {
                 label: node.title,
                 enabled: node.enabled,
                 trailing: node.keybinding != null
-                    ? ClideText(node.keybinding!, fontSize: clideFontSmall, fontFamily: clideMonoFamily, color: ClideTheme.of(ctx).surface.globalTextMuted)
+                    ? ClideText(
+                        node.keybinding!,
+                        fontSize: clideFontSmall,
+                        fontFamily: ClideSettings.fonts.monoOf(context),
+                        color: ClideTheme.of(ctx).surface.globalTextMuted,
+                      )
                     : null,
                 onSelect: () => unawaited(widget.kernel.commands.execute(node.commandId)),
               )