Add OAuth login support and streamline authentication flows

- Introduced `oauthLogin` method in `electron/preload.ts` and backend IPC handlers for OAuth via `BrowserWindow`.
- Replaced web-based OAuth redirection with Electron-specific implementation for Google, Facebook, and Apple.
- Refactored `SocialForm.tsx` to handle OAuth login success and token management via Electron.
- Updated `User`, `QuillSense`, and context methods to include `quill-trial` subscriptions and extended login logic.
- Cleaned up code, removed unused imports, and improved error handling for authentication scenarios.

electron.d.ts

@@ -40,6 +40,14 @@ export interface IElectronAPI {
   // Open external links (browser/native app)
   openExternal: (url: string) => Promise<void>;
 
+  // OAuth login via BrowserWindow
+  oauthLogin: (provider: 'google' | 'facebook' | 'apple', baseUrl: string) => Promise<{
+    success: boolean;
+    code?: string;
+    state?: string;
+    error?: string;
+  }>;
+
   // Offline mode management
   offlinePinSet: (pin: string) => Promise<{ success: boolean; error?: string }>;
   offlinePinVerify: (pin: string) => Promise<{ success: boolean; userId?: string; error?: string }>;