refactor(i18n): route command + settings manifest labels through the catalog (T-462)

Apply the manifest-i18n foundation across every extension: each
CommandContribution (45, command-palette + menu) gains titleKey + i18nNamespace,
and each SettingsCategory/section/field/option gains its key — with the English
text added to the owning extension's catalog. The settings renderer
(settings_category_view + settings_modal) threads the category's i18nNamespace
down and resolves every label/help/option through it; new catalogs created for
view, cli-install, keybindings-ui. No en_US behaviour change — the command
palette, menus, and settings panel now localize from the catalog (D-21).

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

lib/builtin/welcome/src/extension.dart

@@ -26,6 +26,8 @@ class WelcomeExtension extends ClideExtension {
       id: 'workspace.open-project',
       command: 'workspace.open-project',
       title: 'Workspace: Open project…',
+      titleKey: 'command.workspace.open-project',
+      i18nNamespace: id,
       run: (_) async => IpcResponse.ok(id: '', data: const {'note': 'project picker lands in a later tier'}),
     ),
   ];