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-conversation/package.json

@@ -24,7 +24,7 @@
   },
   "dshClient": {
     "inject": [
-      "@deepseek-ai/dsh-client-i18n",
+      "@deepseek-ai/dsh-client-locale",
       "@deepseek-ai/dsh-client-runtime",
       "@deepseek-ai/dsh-client-ui-layout"
     ],

packages/client/ui-conversation/tests/apply-inject.spec.tsx

@@ -99,7 +99,7 @@ async function bench() {
   ctx.provide('workspaces', workspacesFake)
   const layoutFake = { openDetails: vi.fn(), closeDetails: vi.fn() }
   ctx.provide('layout', layoutFake)
-  ctx.provide('i18n', { bind: () => (key: string) => key })
+  ctx.provide('locale', { bind: () => (key: string) => key })
 
   // The AppFrame role: the three conversation-package slots must be declared
   // by a live entry before apply can contribute into them (the stand-in

packages/client/ui-conversation/tests/chat-apply.spec.tsx

@@ -48,7 +48,7 @@ async function bench() {
     sendSession: vi.fn(),
   })
   ctx.provide('layout', { openDetails: vi.fn(), closeDetails: vi.fn() })
-  ctx.provide('i18n', { bind: () => (key: string) => key })
+  ctx.provide('locale', { bind: () => (key: string) => key })
 
   // Declared by ui-layout's root entry in production; a stand-in root
   // occupant declares them here so the contributions land (it consumes

packages/client/ui-conversation/tests/chat-toolview-slot.spec.tsx

@@ -93,7 +93,7 @@ async function bench(nodes: ToolResultNode[]) {
     sendSession: vi.fn(),
   })
   ctx.provide('layout', layout)
-  ctx.provide('i18n', { bind: () => (key: string) => key })
+  ctx.provide('locale', { bind: () => (key: string) => key })
 
   slots.install(createSlotRenderer())
   slots.register({
@@ -212,7 +212,7 @@ describe('registrant load-order seam', () => {
       sendSession: vi.fn(),
     })
     ctx.provide('layout', { openDetails: vi.fn(), closeDetails: vi.fn() })
-    ctx.provide('i18n', { bind: () => (key: string) => key })
+    ctx.provide('locale', { bind: () => (key: string) => key })
     slots.register({
       name: 'root',
       children: {

packages/client/ui-conversation/tsconfig.json

@@ -27,7 +27,7 @@
       "path": "../ui-layout"
     },
     {
-      "path": "../i18n"
+      "path": "../locale"
     },
     {
       "path": "../../support/invariants"