Fix multiple bugs: thumbnail generation, branding settings, categories, theme, feedback icons, upload limit, email errors

Bug fixes included:

#52 - Thumbnail Generation: Added proper parsing of settings values and validation
      of Sharp fit parameter to handle JSON-encoded strings correctly

#61 - Branding Settings Not Persisting: Added _parseBoolean helper for reliable
      boolean parsing, added hide_powered_by option for white-label support

#55 - Categories Not Applied: Fixed category update logic to properly handle
      numeric category IDs, added updated_at timestamp, improved cache invalidation

#59/#56 - Gallery Layout & Apply Theme: Set isPreviewMode=true so theme changes
      immediately propagate to parent state, hidden redundant Apply button

#58 - Feedback Icons Show When Disabled: Added feedbackEnabled check to comment
      and like buttons in MasonryGalleryLayout and GridGalleryLayout

#57 - Upload Limit 100MB: Increased body parser limit from 100MB to 500MB to
      support larger batch uploads

#54 - Wrong Error Message: Enhanced email error handling with specific error
      codes and translation keys for better user feedback

backend/src/routes/adminEmail.js

@@ -173,26 +173,57 @@ router.post('/test', adminAuth, async (req, res) => {
   } catch (error) {
     console.error('Test email error:', error);
     console.error('Error stack:', error.stack);
-    
-    // Provide more specific error messages
-    let errorMessage = 'Failed to send test email';
+
+    // Provide more specific error messages with translation keys
+    let errorMessage = 'Error sending email';
+    let errorKey = 'email.errors.sendFailed';
     let details = error.message;
-    
+    let detailsKey = 'email.errors.unknownError';
+
     if (error.code === 'ECONNREFUSED') {
       errorMessage = 'Failed to connect to SMTP server';
+      errorKey = 'email.errors.connectionRefused';
       details = 'Please check your SMTP host and port settings';
+      detailsKey = 'email.errors.checkHostPort';
     } else if (error.code === 'EAUTH') {
       errorMessage = 'SMTP authentication failed';
+      errorKey = 'email.errors.authFailed';
       details = 'Please check your SMTP username and password';
+      detailsKey = 'email.errors.checkCredentials';
     } else if (error.code === 'ESOCKET') {
-      errorMessage = 'Network error';
+      errorMessage = 'Network error connecting to SMTP server';
+      errorKey = 'email.errors.networkError';
       details = 'Could not establish connection to SMTP server';
+      detailsKey = 'email.errors.connectionFailed';
+    } else if (error.code === 'ETIMEDOUT') {
+      errorMessage = 'Connection to SMTP server timed out';
+      errorKey = 'email.errors.timeout';
+      details = 'The server took too long to respond. Please check your network and SMTP settings.';
+      detailsKey = 'email.errors.timeoutDetails';
+    } else if (error.code === 'ENOTFOUND') {
+      errorMessage = 'SMTP server not found';
+      errorKey = 'email.errors.serverNotFound';
+      details = 'The SMTP host could not be resolved. Please verify the hostname.';
+      detailsKey = 'email.errors.checkHostname';
+    } else if (error.responseCode >= 500) {
+      errorMessage = 'SMTP server error';
+      errorKey = 'email.errors.serverError';
+      details = `Server returned error code ${error.responseCode}`;
+      detailsKey = 'email.errors.serverErrorDetails';
+    } else if (error.responseCode >= 400) {
+      errorMessage = 'Email rejected by server';
+      errorKey = 'email.errors.rejected';
+      details = error.response || 'The email was rejected. Check recipient address and settings.';
+      detailsKey = 'email.errors.rejectedDetails';
     }
-    
-    res.status(500).json({ 
+
+    res.status(500).json({
       error: errorMessage,
+      errorKey: errorKey,
       details: details,
-      code: error.code
+      detailsKey: detailsKey,
+      code: error.code,
+      responseCode: error.responseCode
     });
   }
 });