feat: add privacy mode, thinking levels, PWA support, and i18n

- Add privacy mode to hide IP and user preferences from AI requests
- Add model thinking levels (low/medium/high) for context analysis depth
- Add PWA support with service worker, manifest, and app icons
- Add SettingsPanel for user preferences (theme, background, language)
- Add i18n translations for en/zh/ja/ko/de/fr
- Add Pinia store for centralized settings management
- Update backend to support user preferences and thinking levels
- Update config to use absolute API URLs

src/main.js

@@ -2,7 +2,18 @@ import { createApp } from 'vue'
 import App from './App.vue'
 import './style.css'
 
+import { createPinia } from 'pinia'
 import '@milkdown/crepe/theme/common/style.css'
 import '@milkdown/crepe/theme/frame.css'
 
-createApp(App).mount('#app')
+const app = createApp(App)
+app.use(createPinia())
+app.mount('#app')
+
+if (import.meta.env.PROD && 'serviceWorker' in navigator) {
+  window.addEventListener('load', () => {
+    navigator.serviceWorker.register('/sw.js').catch((error) => {
+      console.error('Service worker registration failed:', error)
+    })
+  })
+}