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

preload.js

@@ -1,27 +1,124 @@
 const { contextBridge, ipcRenderer } = require("electron");
 
+/**
+ * Exposes the main application API to the renderer process.
+ *
+ * This API acts as a secure bridge between the renderer and the
+ * Electron main process using IPC (Inter-Process Communication).
+ * All calls are explicitly whitelisted.
+ */
 contextBridge.exposeInMainWorld("electronAPI", {
+
+  /**
+   * Returns the default system download directory.
+   */
   getDefaultDownloadPath: () => ipcRenderer.invoke("get-default-download-path"),
+
+  /**
+   * Opens a native dialog allowing the user to select a download folder.
+   */
   selectDownloadFolder: () => ipcRenderer.invoke("select-download-folder"),
+
+  /**
+   * Sends download progress value to the main process (used for taskbar / UI sync).
+   *
+   * @param {number} percent - Download progress percentage (0–100)
+   */
   setProgress: (percent) => ipcRenderer.send("set-progress", percent),
+
+  /**
+   * Retrieves application feature flags (runtime configuration).
+   */
   getFeatures: () => ipcRenderer.invoke("features"),
-  setFeature: (key, value) => ipcRenderer.invoke("set-feature", { key, value }),
+
+  /**
+   * Updates a feature flag dynamically at runtime.
+   *
+   * @param {string} key - Feature name
+   * @param {any} value - Feature value
+   */
+  setFeature: (key, value) =>
+    ipcRenderer.invoke("set-feature", { key, value }),
+
+  /**
+   * Returns the current application version.
+  */
   getVersion: () => ipcRenderer.invoke("version"),
-  getValidatedDownloadPath: (path) => ipcRenderer.invoke("validate-download-path", path),
+
+  /**
+   * Validates a download path before using it for file operations.
+   *
+   * @param {string} path - Path to validate
+   */
+  getValidatedDownloadPath: (path) =>
+    ipcRenderer.invoke("validate-download-path", path),
+
+  /**
+   * Retrieves available themes from the filesystem or config layer.
+   */
   getThemes: () => ipcRenderer.invoke("get-themes"),
-  reloadThemes: () => ipcRenderer.invoke("reload-themes")
+
+  /**
+   * Forces a reload of theme files (useful after modification/import).
+   */
+  reloadThemes: () => ipcRenderer.invoke("reload-themes"),
 });
 
-// Contrôles de fenêtre et outils custom pour la topbar
+
+/**
+ * Exposes window control and developer utilities for the custom topbar UI.
+ *
+ * These methods forward commands to the Electron main process via IPC.
+ */
 contextBridge.exposeInMainWorld("topbarAPI", {
+
+  /**
+   * Minimizes the application window.
+   */
   minimize: () => ipcRenderer.send("window-minimize"),
+
+  /**
+   * Toggles maximize/restore state of the application window.
+   */
   maximize: () => ipcRenderer.send("window-maximize"),
+
+  /**
+   * Closes the application window.
+   */
   close: () => ipcRenderer.send("window-close"),
+
+  /**
+   * Opens Chromium DevTools for debugging.
+   */
   openDevTools: () => ipcRenderer.send("open-devtools"),
+
+  /**
+   * Opens application logs directory or log viewer.
+   */
   openLogs: () => ipcRenderer.send("open-logs"),
+
+  /**
+   * Opens the official website or project homepage.
+   */
   openWebsite: () => ipcRenderer.send("open-website"),
+
+  /**
+   * Opens the theme directory or theme editor interface.
+   */
   openTheme: () => ipcRenderer.send("open-theme"),
+
+  /**
+   * Opens project wiki/documentation.
+   */
   openWiki: () => ipcRenderer.send("open-wiki"),
+
+  /**
+   * Opens the workshop or external content library.
+   */
   openWorkshop: () => ipcRenderer.send("open-workshop"),
-  openConfig: () => ipcRenderer.send("open-config")
-});
+
+  /**
+   * Opens configuration/settings panel.
+   */
+  openConfig: () => ipcRenderer.send("open-config"),
+});