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/associations.js

@@ -6,6 +6,7 @@ import Room from './chat/room.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 UserParamType from './type/user_param.js';
 import UserRightType from './type/user_right.js';
 import UserRight from './community/user_right.js';
@@ -182,6 +183,9 @@ export default function setupAssociations() {
   User.hasOne(UserDashboard, { foreignKey: 'userId', as: 'dashboard' });
   UserDashboard.belongsTo(User, { foreignKey: 'userId', as: 'user' });
 
+  User.hasMany(OAuthIdentity, { foreignKey: 'userId', as: 'oauthIdentities' });
+  OAuthIdentity.belongsTo(User, { foreignKey: 'userId', as: 'user' });
+
   UserParamValue.belongsTo(UserParamType, { foreignKey: 'userParamTypeId', as: 'user_param_value_type' });
   UserParamType.hasMany(UserParamValue, { foreignKey: 'userParamTypeId', as: 'user_param_type_value' });