refactor(routes): Phase 3.6-10 - standardize 5 utility routes

- credentials.js (2 deps: credentialManager, asyncHandler)
- backups.js (2 deps: backupManager, asyncHandler)
- license.js (2 deps: licenseManager, asyncHandler)
- errorlogs.js (3 deps: ERROR_LOG_FILE, auditLogger, asyncHandler)
- themes.js (0 deps! Standalone route)

Total: 9 routes refactored so far

dashcaddy-api/routes/themes.js

@@ -1,8 +1,14 @@
 const express = require('express');
 const fs = require('fs');
 const path = require('path');
+const { success } = require('../response-helpers');
 
-module.exports = function(ctx) {
+/**
+ * Themes routes factory
+ * Note: This route does not use asyncHandler - uses synchronous fs operations
+ * @returns {express.Router}
+ */
+module.exports = function() {
   const router = express.Router();
   const THEMES_DIR = process.env.THEMES_DIR || path.join(path.dirname(process.env.SERVICES_FILE || '/app/services.json'), 'themes');
 
@@ -28,7 +34,7 @@ module.exports = function(ctx) {
 
   // Get all user themes
   router.get('/themes', (req, res) => {
-    res.json({ success: true, themes: readAllThemes() });
+    success(res, { themes: readAllThemes() });
   });
 
   // Save a theme (create or update)
@@ -48,7 +54,7 @@ module.exports = function(ctx) {
     if (lightBg) themeData.lightBg = true;
     fs.writeFileSync(path.join(THEMES_DIR, slug + '.json'), JSON.stringify(themeData, null, 2), 'utf8');
 
-    res.json({ success: true, message: name + ' theme saved' });
+    success(res, { message: name + ' theme saved' });
   });
 
   // Delete a theme
@@ -64,7 +70,7 @@ module.exports = function(ctx) {
     const name = data.name || slug;
     fs.unlinkSync(filePath);
 
-    res.json({ success: true, message: name + ' theme deleted' });
+    success(res, { message: name + ' theme deleted' });
   });
 
   return router;