Update documentation for new features and auth improvements

Expanded documentation to cover the new downloads manager, native context menu, OAuth/SSO and WebAuthn compatibility, and user agent strategy. Updated project structure and core concepts to reflect these features and clarified session and popup handling for authentication. Fixed minor typos and improved feature descriptions for clarity.

documentation/PROJECT_STRUCTURE.md

@@ -3,6 +3,7 @@
 This document provides an in-depth look at the project's file and directory structure.
 
 -   **`main.js`**: This is the heart of the Electron application. It's the main process script that controls the application's lifecycle, creates browser windows, and handles all interactions with the operating system.
+    -   Manages native context menu, downloads, and OAuth/WebAuthn-friendly window behavior.
 
 -   **`renderer/`**: This directory contains all the client-side code and assets for the browser's user interface (the renderer process).
     -   **`index.html`**: The main HTML file that serves as the container for the browser's UI, including the tab bar, address bar, and the webview for displaying web content.
@@ -14,12 +15,14 @@ This document provides an in-depth look at the project's file and directory stru
     -   **`gpu-diagnostics.html`**: The page for displaying GPU information.
     -   **`performance.css`**: Styles for the performance monitoring page.
     -   **`icons.js`**, **`icons.json`**: Files related to managing icons within the UI.
+    -   Other pages: downloads UI and settings integrate with main-process IPC.
 
 -   **`preload.js`**: This script is a crucial part of Electron's security model. It runs in a privileged context before the renderer process's web page is loaded. It's used to selectively expose APIs from the main process to the renderer process via the `contextBridge`.
 
 -   **`performance-monitor.js`**: A Node.js module that runs in the main process to track application performance metrics like memory usage and page load times.
 
 -   **`gpu-config.js`** & **`gpu-fallback.js`**: These modules are responsible for managing GPU-related settings. `gpu-config.js` checks the system's GPU capabilities, and `gpu-fallback.js` provides mechanisms to disable or reduce GPU acceleration if problems are detected.
+    -   `start-gpu-safe.bat` starts the app with safer GPU settings on Windows.
 
 -   **`assets/`**: This directory holds all static assets.
     -   **`images/`**: Contains logos, icons, and other images used in the application.
@@ -32,5 +35,6 @@ This document provides an in-depth look at the project's file and directory stru
     -   **`bookmarks.json`**: Stores the user's bookmarks.
     -   **`site-history.json`**: Stores the user's browsing history.
     -   **`search-history.json`**: Stores the user's search history.
+    -   **`bookmarks.backup.json`**: Auto-created backup of bookmarks on save.
 
 -   **`start-gpu-safe.bat`**: A batch script for Windows users to start the application in a GPU-safe mode.