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/server.js

@@ -2,7 +2,7 @@ const express = require("express");
 const path = require("path");
 const { logger, logSessionEnd } = require("./logger");
 const config = require("../config");
-const { rateLimite } = require("./helpers/rateLimit.helpers");
+const { rateLimit } = require("./helpers/rateLimit.helpers");
 
 const app = express();
 
@@ -14,10 +14,18 @@ app.use(express.static(path.join(__dirname, "../public")));
 // Routes
 app.use("/download", require("./routes/download.route"));
 app.use("/info",     require("./routes/info.route"));
-app.get("/", rateLimite, (req, res) => {
+app.get("/", rateLimit, (req, res) => {
   res.sendFile(path.join(__dirname, "../public/index.html"));
 });
 
+/**
+ * Initializes and starts the Express HTTP server.
+ * 
+ * - Binds the server to `config.applicationPort`
+ * - Resolves with the HTTP server instance on successful startup
+ * - Rejects on server binding or runtime errors
+ * - Registers SIGINT/SIGTERM handlers for graceful shutdown
+ */
 async function startServer() {
   return new Promise((resolve, reject) => {
     const server = app.listen(config.applicationPort, () => {
@@ -30,6 +38,12 @@ async function startServer() {
       reject(err);
     });
 
+    /**
+     * Clean exit function
+     *  - Stop Log 
+     *  - Stop Express Server
+     *  - Stop Electron App 
+     */
     const gracefulExit = () => {
       logSessionEnd();
       server.close(() => {