Add i18n foundation and translations (#1027)

* feat: add i18n foundation

* feat: localize sessions sidebar

* Localize multirun/scheduled tasks and fix dialog dropdown interactions

* localize git sidebar surface and add zh-CN keys

* feat(ui): localize context panel, diff/plan views, and context sidebar content

* fix(config): resolve user config home via fs/home before embedded home

* localize header/chat UI and complete model/worktree panel strings

* localize worktree + github issue/pr dialog flows

* localize settings sections and split settings i18n dictionaries

* localize additional settings sections and sidebars

* localize more settings pages and dialogs

* fix settings select trigger localization

* localize tunnel settings ui surface

* localize additional settings sections

* localize keyboard shortcuts labels in settings

* localize terminal and utility dialogs surfaces

* feat(i18n): localize remaining UI strings

* Add Ukrainian locale

* Add Spanish locale

* Add Brazilian Portuguese locale

* Polish locale translations

packages/ui/src/main.tsx

@@ -12,6 +12,7 @@ import { startAppearanceAutoSave } from './lib/appearanceAutoSave'
 import { applyPersistedDirectoryPreferences } from './lib/directoryPersistence'
 import { startTypographyWatcher } from './lib/typographyWatcher'
 import { startModelPrefsAutoSave } from './lib/modelPrefsAutoSave'
+import { initializeLocale, I18nProvider } from './lib/i18n'
 import type { RuntimeAPIs } from './lib/api/types'
 
 declare global {
@@ -24,6 +25,8 @@ const runtimeAPIs = (typeof window !== 'undefined' && window.__OPENCHAMBER_RUNTI
   throw new Error('Runtime APIs not provided for legacy UI entrypoint.');
 })();
 
+initializeLocale();
+
 // Initialize settings asynchronously — the app renders with defaults first
 // and hydrates once persisted preferences are applied. Users with non-default
 // themes may briefly see default appearance on cold start; accepted trade-off
@@ -52,12 +55,14 @@ if (!rootElement) {
 
 createRoot(rootElement).render(
   <StrictMode>
-    <ThemeSystemProvider>
-      <ThemeProvider>
-        <SessionAuthGate>
-          <App apis={runtimeAPIs} />
-        </SessionAuthGate>
-      </ThemeProvider>
-    </ThemeSystemProvider>
+    <I18nProvider>
+      <ThemeSystemProvider>
+        <ThemeProvider>
+          <SessionAuthGate>
+            <App apis={runtimeAPIs} />
+          </SessionAuthGate>
+        </ThemeProvider>
+      </ThemeSystemProvider>
+    </I18nProvider>
   </StrictMode>,
 );