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/widgets/src/clide_pty_view.dart

@@ -4,6 +4,8 @@ import 'package:clide/widgets/src/typography.dart';
 import 'package:flutter/widgets.dart';
 import 'package:clide/src/terminal/terminal.dart';
 
+import 'clide_settings.dart';
+
 /// Theme-aware terminal view. Wraps xterm.dart's [TerminalView] with
 /// clide token bindings, JetBrainsMono as the face, and a Semantics
 /// wrapper that exposes the pane as a live region with the terminal's
@@ -42,7 +44,7 @@ class ClidePtyView extends StatelessWidget {
           focusNode: focusNode,
           autofocus: autofocus,
           theme: _buildTheme(tokens),
-          textStyle: TerminalStyle(fontSize: fontSize, fontFamily: clideMonoFamily, fontFamilyFallback: clideMonoFamilyFallback),
+          textStyle: TerminalStyle(fontSize: fontSize, fontFamily: ClideSettings.fonts.monoOf(context), fontFamilyFallback: clideMonoFamilyFallback),
           padding: const EdgeInsets.all(2),
           backgroundOpacity: 1,
           cursorType: TerminalCursorType.block,