docs(i18n): record D-102 (i18n routing) + ui-design skill rule

Document the T-462 i18n architecture: ext-id namespaces auto-loaded on
activation, a 'core' catalog for framework chrome, the null-safe
ClideSettings.i18n read facade, contribution titleKey/labelKey fields, and the
assets/i18n/<locale>/<namespace>.json locale-dir layout. Add the "route
user-facing strings through the catalog" rule to the ui-design skill.

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

governance/README.md

@@ -143,6 +143,7 @@ You might also want, project-permitting:
 - [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_
+- [D-102: i18n routing — ext-id namespaces, `core` catalog, ClideSettings.i18n facade, contribution keys](decisions/accessibility.md#d-102-i18n-routing--ext-id-namespaces-core-catalog-clidesettingsi18n-facade-contribution-keys) — _accessibility_
 
 ## Open questions