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/getBrowser.helpers.js

@@ -4,10 +4,33 @@ const path = require("path");
 const notify = require("./notify.helpers")
 const { logger } = require("../logger");
 
+/**
+ * Detects the first supported browser installed on the system.
+ *
+ * The detected browser is used by yt-dlp to import authentication
+ * cookies when required by certain platforms.
+ *
+ * Currently, Firefox is the only browser officially supported
+ * by the application.
+ *
+ * If no supported browser is found:
+ * - A warning is logged
+ * - A notification is displayed to the user
+ * - "firefox" is returned as a fallback to allow yt-dlp to
+ *   handle the error gracefully without crashing the application
+ *
+ * @returns {string} The detected browser identifier.
+ */
 function getUserBrowser() {
   const userProfile = os.homedir();
 
-  // List of browsers supported by yt-dlp (Currently I can only guarantee Firefox, Sorry)
+  /**
+   * Browsers supported by yt-dlp cookie extraction.
+   *
+   * Only Firefox is currently enabled and tested.
+   * Additional browsers can be enabled in the future
+   * once compatibility has been verified.
+   */
   const browsers = [
     { name: "firefox", path: path.join(userProfile, "AppData", "Roaming", "Mozilla", "Firefox", "Profiles") },
     // { name: "chrome", path: path.join(userProfile, "AppData", "Local", "Google", "Chrome", "User Data", "Default") },
@@ -19,7 +42,7 @@ function getUserBrowser() {
     // { name: "whale", path: path.join(userProfile, "AppData", "Local", "Naver", "Naver Whale", "User Data", "Default") }
   ];
 
-  // Search for an available browser
+  // Search for the first available browser profile.
   for (const browser of browsers) {
     if (fs.existsSync(browser.path)) {
       logger.info(`Browser found: ${browser.name}`);
@@ -27,12 +50,12 @@ function getUserBrowser() {
     }
   }
 
-  // No browser found - notify user
+  // No supported browser found => Notify User
   logger.warn("No supported browser found on the system");
   notify.notifyFirefoxBrowserMissing();
   
-  // Fallback: return "Firefox" to let YT-DLP manage error
-  // this avoid app crash
+  // Fallback to Firefox and let yt-dlp handle the error gracefully.
+  // This prevents the application from crashing
   return "firefox";
 }