Refactor email verification to use JSON responses instead of redirects

- Replace server-side redirects with JSON API responses for better error handling
- Add support for partial success when Keycloak update fails but token is valid
- Improve error messages with specific status codes (410 for expired, 409 for already used)
- Extract email from API response instead of URL query parameters
- Enable client-side navigation with proper error state management

server/api/auth/verify-email.get.ts

@@ -18,6 +18,8 @@ export default defineEventHandler(async (event) => {
     // Update user verification status in Keycloak
     const { createKeycloakAdminClient } = await import('~/server/utils/keycloak-admin');
     const keycloak = createKeycloakAdminClient();
+    
+    let partialSuccess = false;
 
     try {
       await keycloak.updateUserProfile(userId, {
@@ -29,27 +31,38 @@ export default defineEventHandler(async (event) => {
 
       console.log('[verify-email] Successfully verified user:', userId, 'email:', email);
       
-      // Redirect to success page
-      return sendRedirect(event, '/auth/verify-success?email=' + encodeURIComponent(email), 302);
-      
     } catch (keycloakError: any) {
       console.error('[verify-email] Keycloak update failed:', keycloakError.message);
-      
       // Even if Keycloak update fails, consider verification successful if token was valid
       // This prevents user frustration due to backend issues
-      return sendRedirect(event, '/auth/verify-success?email=' + encodeURIComponent(email) + '&warning=partial', 302);
+      partialSuccess = true;
     }
 
+    // Return JSON response for client-side navigation
+    return {
+      success: true,
+      data: {
+        userId,
+        email,
+        partialSuccess
+      }
+    };
+
   } catch (error: any) {
     console.error('[verify-email] Verification failed:', error.message);
 
-    // Handle different error types with appropriate redirects
+    // Return error response
     if (error.message?.includes('expired')) {
-      return sendRedirect(event, '/auth/verify-expired', 302);
+      throw createError({
+        statusCode: 410,
+        statusMessage: 'Verification link has expired. Please request a new one.'
+      });
     } else if (error.message?.includes('already used') || error.message?.includes('not found')) {
-      return sendRedirect(event, '/auth/verify-expired?reason=used', 302);
+      throw createError({
+        statusCode: 409,
+        statusMessage: 'This verification link has already been used or is invalid.'
+      });
     } else {
-      // For other errors, show a generic error page
       throw createError({
         statusCode: 400,
         statusMessage: error.message || 'Invalid verification link'