Add OAuth integration for multiple providers and implement user linking

- Created OAuth credentials setup guide for Google, Microsoft, Keycloak, ORY, and ZITADEL.
- Added migration for oauth_identity table to store OAuth identities linked to users.
- Implemented OAuthIdentity model for managing OAuth identities in the database.
- Developed oauthService to handle OAuth login, user creation, and identity linking.
- Created OAuthCallbackView and OAuthUserCallbackView components for handling OAuth responses in the frontend.
- Added error handling and user feedback during the OAuth process.

backend/models/index.js

@@ -8,6 +8,7 @@ import WidgetType from './type/widget_type.js';
 import User from './community/user.js';
 import UserParam from './community/user_param.js';
 import UserDashboard from './community/user_dashboard.js';
+import OAuthIdentity from './community/oauth_identity.js';
 import Login from './logs/login.js';
 import UserRight from './community/user_right.js';
 import InterestType from './type/interest.js';
@@ -168,6 +169,7 @@ const models = {
   User,
   UserParam,
   UserDashboard,
+  OAuthIdentity,
   Login,
   UserRight,
   InterestType,