Add E2E tests for OAuth authentication flows and provider integrations

- Implemented comprehensive E2E tests for OAuth buttons on login and register pages, including Google and GitHub provider interactions.
- Verified OAuth provider buttons' visibility, icons, and proper API integration with mock endpoints.
- Added button interaction tests to ensure correct API calls for authorization and state handling.
- Updated `playwright.config.ts` to include the new `auth-oauth.spec.ts` in test configurations.
- Extended mock handlers in `overrides.ts` and `auth.ts` to support OAuth-specific API workflows and demo scenarios.

frontend/src/mocks/handlers/overrides.ts

@@ -14,6 +14,7 @@
 import { http, HttpResponse, delay } from 'msw';
 import { generateMockToken } from '../utils/tokens';
 import { validateCredentials, setCurrentUser, currentUser } from '../data/users';
+import config from '@/config/app.config';
 
 const API_BASE_URL = process.env.NEXT_PUBLIC_API_BASE_URL || 'http://localhost:8000';
 const NETWORK_DELAY = 300; // ms - simulate realistic network delay
@@ -101,4 +102,84 @@ export const overrideHandlers = [
       expires_in: 900,
     });
   }),
+
+  /**
+   * OAuth Providers Override
+   * Returns list of available OAuth providers for demo mode
+   */
+  http.get(`${API_BASE_URL}/api/v1/oauth/providers`, async () => {
+    await delay(NETWORK_DELAY);
+
+    return HttpResponse.json({
+      enabled: true,
+      providers: [
+        { provider: 'google', name: 'Google' },
+        { provider: 'github', name: 'GitHub' },
+      ],
+    });
+  }),
+
+  /**
+   * OAuth Authorization URL Override
+   * Returns mock authorization URL (in demo mode, this won't actually redirect)
+   */
+  http.get(`${API_BASE_URL}/api/v1/oauth/authorize/:provider`, async ({ params }) => {
+    await delay(NETWORK_DELAY);
+
+    const { provider } = params;
+
+    // In demo mode, we return a mock URL that will show a demo message
+    return HttpResponse.json({
+      authorization_url: `${config.app.url}/en/login?demo_oauth=${provider}`,
+      state: `demo-state-${Date.now()}`,
+    });
+  }),
+
+  /**
+   * OAuth Callback Override
+   * Handles mock OAuth callback in demo mode
+   */
+  http.post(`${API_BASE_URL}/api/v1/oauth/callback/:provider`, async ({ params }) => {
+    await delay(NETWORK_DELAY);
+
+    const { provider } = params;
+
+    // Create a demo user based on the provider
+    const demoOAuthUser = {
+      id: `oauth-demo-${Date.now()}`,
+      email: `demo.${provider}@example.com`,
+      first_name: 'Demo',
+      last_name: `${provider === 'google' ? 'Google' : 'GitHub'} User`,
+      phone_number: null,
+      is_active: true,
+      is_superuser: false,
+      created_at: new Date().toISOString(),
+      updated_at: new Date().toISOString(),
+      last_login: new Date().toISOString(),
+      organization_count: 0,
+    };
+
+    setCurrentUser(demoOAuthUser);
+
+    return HttpResponse.json({
+      access_token: generateMockToken('access', demoOAuthUser.id),
+      refresh_token: generateMockToken('refresh', demoOAuthUser.id),
+      token_type: 'bearer',
+      expires_in: 900,
+      is_new_user: true,
+    });
+  }),
+
+  /**
+   * OAuth Accounts Override
+   * Returns linked OAuth accounts for the current user
+   */
+  http.get(`${API_BASE_URL}/api/v1/oauth/accounts`, async () => {
+    await delay(NETWORK_DELAY);
+
+    // In demo mode, return empty accounts (user can "link" them)
+    return HttpResponse.json({
+      accounts: [],
+    });
+  }),
 ];