refactor: add full documentation and fix theme loading robustness

- Add JSDoc comments across frontend and backend modules
- Improve code readability and maintainability with consistent documentation style
- Document Electron IPC handlers, UI utilities, and theme system
- Add missing function/class documentation in theme loader and app services
- Minor structural improvements and cleanup across Electron main process modules
- Minor fixes on variable names

server/helpers/validation.helpers.js

@@ -1,21 +1,43 @@
 const path = require("path");
 
-function isValidUrl(url) { 
-  try { 
-      new URL(url); 
-      return true; 
-      
-    } catch { 
-      return false; 
-    } 
+/**
+ * Validates whether the provided string is a well-formed URL.
+ *
+ * The validation relies on the native URL constructor and
+ * returns `true` only if the value can be successfully parsed.
+ *
+ * @param {string} url - URL to validate.
+ * @returns {boolean} True if the URL is valid, otherwise false.
+ */
+function isValidUrl(url) {
+  try {
+    new URL(url);
+    return true;
 
+  } catch {
+    return false;
+  }
 }
 
+/**
+ * Validates whether a folder path is considered safe for
+ * file operations.
+ *
+ * Security checks:
+ * - Rejects empty or very short paths.
+ * - Resolves the absolute path before validation.
+ * - Prevents access to sensitive Windows system directories.
+ *
+ * @param {string} folder - Folder path to validate.
+ * @returns {boolean} True if the path is considered safe, otherwise false.
+ */
 function isSafePath(folder) {
   if (!folder || folder.length < 3) return false;
+
   const unsafe = ["System32", "\\Windows"];
   const resolved = path.resolve(folder);
+
   return !unsafe.some(u => resolved.includes(u));
 }
 
-module.exports = { isValidUrl, isSafePath };
+module.exports = { isValidUrl, isSafePath };