feat(gui): settings panel with locale and theme preferences

Add the browser Settings surface as slot-composed plugins over new
preference services:

- Rename dsh-client-i18n to dsh-client-locale (locale is the domain
  name); LocaleService adds getLocale()/setLocale(id), immutable
  snapshots, a locale/change event, and dsh.locale persistence.
- ThemeService owns the light/dark/system preference (default system),
  resolves system via prefers-color-scheme, publishes theme/change
  snapshots, persists dsh.theme, and no longer touches the DOM;
  ui-layout's ThemePresenter applies resolved snapshots
  (body[data-ds-dark-theme] + alias tokens) and cleans up on dispose.
- ui-sidebar drops the phase-1 settings dropdown/modal; the foot renders
  the new sidebar.settings slot with the column state.
- New ui-settings shell occupies sidebar.settings: foot trigger row and
  the centered 1080x700 panel (figma 501:29947) with 24% mask, close
  button / mask click / Escape all closing, and a 188px nav projected
  from the settings.section list slot it declares. Nav labels are
  registrant-localized; sections re-register on locale change, so the
  ledger version is the shell's only subscription.
- ui-settings-general registers the General section: Permission and
  Tool Call skeletons, live Language (locale menu) and Appearance
  (Light/Dark/System cubes following the persisted preference); its
  slot store mirrors both service snapshots via apply-side listeners.
- ui-settings-models registers the Models nav entry with an empty
  content column.
- Portaled menus pin z-index above modal overlays (a menu anchored
  inside the settings dialog rendered underneath it and was
  unclickable).
- theme/data/list-pen icons in ui-primitives; settings copy ships as
  zh/en dictionaries; fixture manifests gain the settings rows.

packages/client/ui-theme/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@deepseek-ai/dsh-client-ui-theme",
-  "description": "Theme plugin: ThemeService (apply = toggle body[data-ds-dark-theme]), --dsw-* token base stylesheets",
+  "description": "Theme plugin: ThemeService (light/dark/system preference, prefers-color-scheme resolution, theme/change snapshots; no DOM), --dsw-* token base stylesheets",
   "version": "0.0.1",
   "private": true,
   "type": "module",
@@ -44,5 +44,9 @@
     "lib/types/**/*.d.ts",
     "lib/types/**/*.d.ts.map",
     "src"
-  ]
+  ],
+  "scripts": {
+    "bundle": "tsdown",
+    "watch": "tsdown --watch"
+  }
 }