i18n and UI fix

.sisyphus/evidence/task-04-store-compiled.txt

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+# Task 04: Locale Store - Compilation Evidence
+
+## Date: 2026-03-13
+
+## Files Created
+- src/renderer/src/stores/localeStore.ts
+
+## Verification
+
+### TypeScript Check
+```bash
+npx tsc --noEmit
+# Result: PASSED (no errors)
+```
+
+### Store Implementation
+- Uses Zustand with persist middleware
+- Imports LocaleCode and DEFAULT_LOCALE from @shared/types/locale
+- Persists only the locale state value (partialize pattern)
+- Exports useLocaleStore hook
+
+### State Shape
+```typescript
+interface LocaleState {
+  locale: LocaleCode;          // "zh-CN" | "ja-JP" | "en-US"
+  setLocale: (locale: LocaleCode) => void;
+}
+```
+
+### Default Value
+- locale: "zh-CN" (from DEFAULT_LOCALE constant)
+
+## Status: COMPLETED