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>

governance/README.md

@@ -142,6 +142,7 @@ You might also want, project-permitting:
 - [D-98: Remote-tool contract + connect preflight](decisions/architecture.md#d-98-remote-tool-contract--connect-preflight) — _architecture_
 - [D-99: Remote session identity keyed on (host, workspace)](decisions/architecture.md#d-99-remote-session-identity-keyed-on-host-workspace) — _architecture_
 - [D-100: Fence `dart:ffi` behind conditional imports + web stubs to keep the web/WASM target compiling](decisions/tooling.md#d-100-fence-dartffi-behind-conditional-imports--web-stubs-to-keep-the-webwasm-target-compiling) — _tooling_
+- [D-101: ClideSettings — one live-preferences access facade](decisions/architecture.md#d-101-clidesettings--one-live-preferences-access-facade) — _architecture_
 
 ## Open questions