feat: Add OAuth 2.0 / OIDC SSO login support

- Add OAuth SSO provider configuration types (OAuthSsoProviderConfig, OAuthSsoConfig)
- Create OAuth SSO service with support for Google, Microsoft, GitHub, and custom OIDC providers
- Implement OAuth SSO controller with endpoints for SSO configuration, login initiation, and callback handling
- Add routes for /api/auth/sso/* endpoints
- Update User entity and DAOs to support OAuth-linked accounts (oauthProvider, oauthSubject, email, displayName, avatarUrl)
- Update SystemConfig entity to include oauthSso field
- Update migration utility to handle OAuth SSO configuration and user fields
- Add OAuth callback page for frontend token handling
- Update LoginPage with SSO provider buttons and hybrid auth support
- Add i18n translations for OAuth SSO (English and Chinese)
- Add comprehensive tests for OAuth SSO service (13 new tests)

Co-authored-by: samanhappy <2755122+samanhappy@users.noreply.github.com>

locales/en.json

@@ -840,5 +840,25 @@
     "internalError": "Internal Error",
     "internalErrorMessage": "An unexpected error occurred while processing the OAuth callback.",
     "closeWindow": "Close Window"
+  },
+  "oauthSso": {
+    "errors": {
+      "providerIdRequired": "Provider ID is required",
+      "providerNotFound": "OAuth provider not found",
+      "missingState": "Missing OAuth state parameter",
+      "missingCode": "Missing authorization code",
+      "invalidState": "Invalid or expired OAuth state",
+      "authFailed": "OAuth authentication failed",
+      "userNotProvisioned": "User not found and auto-provisioning is disabled"
+    },
+    "signInWith": "Sign in with {{provider}}",
+    "orContinueWith": "Or continue with",
+    "continueWithProvider": "Continue with {{provider}}",
+    "loginWithSso": "Login with SSO",
+    "providers": {
+      "google": "Google",
+      "microsoft": "Microsoft",
+      "github": "GitHub"
+    }
   }
 }