feat(settings): add home content customization and config injection

- Add home_content setting for custom homepage (HTML or iframe URL)
- Inject public settings into index.html to eliminate page flash
- Support ETag caching with automatic invalidation on settings update
- Add Vite plugin for dev mode settings injection
- Refactor HomeView to use appStore instead of local API calls

frontend/src/main.ts

@@ -6,7 +6,20 @@ import i18n from './i18n'
 import './style.css'
 
 const app = createApp(App)
-app.use(createPinia())
+const pinia = createPinia()
+app.use(pinia)
+
+// Initialize settings from injected config BEFORE mounting (prevents flash)
+// This must happen after pinia is installed but before router and i18n
+import { useAppStore } from '@/stores/app'
+const appStore = useAppStore()
+appStore.initFromInjectedConfig()
+
+// Set document title immediately after config is loaded
+if (appStore.siteName && appStore.siteName !== 'Sub2API') {
+  document.title = `${appStore.siteName} - AI API Gateway`
+}
+
 app.use(router)
 app.use(i18n)