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/notify.helpers.js

@@ -1,8 +1,19 @@
 const { Notification, shell } = require("electron");
 const { iconPaths } = require("./path.helpers");
+const { logger } = require("../logger");
 
+/**
+ * Displays a system notification when a download completes successfully.
+ *
+ * If enabled, clicking the notification opens the download folder
+ * using the system file explorer.
+ *
+ * @param {string} folder - Path to the completed download folder.
+ * @param {boolean} notifyEnabled - Whether notifications are enabled in config.
+ */
 function notifyDownloadFinished(folder, notifyEnabled = true) {
   if (!notifyEnabled) return;
+  if (!folder) return;
   
   const notif = new Notification({
     title: "Freedom Loader",
@@ -14,6 +25,15 @@ function notifyDownloadFinished(folder, notifyEnabled = true) {
   notif.show();
 }
 
+/**
+ * Displays a notification when browser cookies cannot be extracted.
+ *
+ * This usually indicates:
+ * - User is not logged in to the browser
+ * - Browser profile is inaccessible
+ *
+ * Clicking the notification opens a tutorial link.
+ */
 function notifyCookiesBrowserError(){
   const notif = new Notification({
     title: "Cookies Error",
@@ -21,23 +41,41 @@ function notifyCookiesBrowserError(){
     icon: iconPaths.error,
   });
 
-  notif.on("click", () => shell.openExternal("https://youtube.com/shorts/cN9f4s1Mf88?si=519QCVd_-fzJqRf1"));
+  notif.on("click", () =>
+    shell.openExternal(
+      "https://youtube.com/shorts/cN9f4s1Mf88?si=519QCVd_-fzJqRf1"
+    )
+  );
+
   notif.show();
 }
 
-function notifyFirefoxBrowserMissing(){
+/**
+ * Displays a notification when Firefox is not detected
+ * on the user system.
+ *
+ * This is required for cookie extraction via yt-dlp.
+ *
+ * Clicking the notification opens an installation guide.
+ */
+function notifyFirefoxBrowserMissing() {
   const notif = new Notification({
     title: "Firefox Missing",
     body: "Firefox was not found on your system. Click here to follow the installation guide",
     icon: iconPaths.error,
   });
 
-  notif.on("click", () => shell.openExternal("https://youtube.com/shorts/cN9f4s1Mf88?si=519QCVd_-fzJqRf1"))
+  notif.on("click", () =>
+    shell.openExternal(
+      "https://youtube.com/shorts/cN9f4s1Mf88?si=519QCVd_-fzJqRf1"
+    )
+  );
+
   notif.show();
 }
 
 module.exports = {
-  notifyDownloadFinished, 
+  notifyDownloadFinished,
   notifyCookiesBrowserError,
-  notifyFirefoxBrowserMissing
+  notifyFirefoxBrowserMissing,
 };