feat(dashboard): add i18n support with zh/en/ja/ko locales

- Add react-i18next + i18next + i18next-browser-languagedetector
- Create i18n config (singleton import) with zh/en/ja/ko JSON locale files
- Add language switcher Globe dropdown in Header topbar
- Replace all hardcoded Chinese strings in:
  - Layout (Header, Sidebar, NavItem, Layout, constants)
  - Settings (index, AppearanceTab, SecurityTab, OtherTab, AboutTab)
  - Auth page (auth.tsx)
  - Search dialog (searchItems via useMemo + t())
  - Restart overlay (getStatusConfig accepts t param)
  - Error boundary (ErrorFallback, ErrorDetails function components)
  - HTTP warning banner
- localStorage key: maibot-locale
- Compatible with Electron

dashboard/package.json

@@ -36,7 +36,10 @@
       "target": [
         {
           "target": "dmg",
-          "arch": ["x64", "arm64"]
+          "arch": [
+            "x64",
+            "arm64"
+          ]
         }
       ],
       "icon": "electron/resources/icon.icns",
@@ -46,7 +49,9 @@
       "target": [
         {
           "target": "nsis",
-          "arch": ["x64"]
+          "arch": [
+            "x64"
+          ]
         }
       ],
       "icon": "electron/resources/icon.ico"
@@ -55,7 +60,9 @@
       "target": [
         {
           "target": "AppImage",
-          "arch": ["x64"]
+          "arch": [
+            "x64"
+          ]
         }
       ],
       "icon": "electron/resources/icon.png",
@@ -130,12 +137,15 @@
     "dagre": "^0.8.5",
     "date-fns": "^4.1.0",
     "html-to-image": "^1.11.13",
+    "i18next": "^25.8.13",
+    "i18next-browser-languagedetector": "^8.2.1",
     "idb": "^8.0.3",
     "katex": "^0.16.27",
     "lucide-react": "^0.556.0",
     "react": "^19.2.1",
     "react-day-picker": "^9.12.0",
     "react-dom": "^19.2.1",
+    "react-i18next": "^16.5.4",
     "react-joyride": "^2.9.3",
     "react-markdown": "^10.1.0",
     "reactflow": "^11.11.4",