Implement complete native menu system with keyboard accelerators

This commit establishes a comprehensive native menu system for the Tauri application, bringing it to parity with the Electron implementation and enabling full keyboard shortcut support.

## Key Features Added

**Native Menu System:**
- Complete menu bar with File, Edit, View, and Window menus
- Platform-specific adaptations (macOS app menu, Windows/Linux quit behavior)
- Full menu event handling system with proper window management

**Keyboard Accelerators:**
- CmdOrCtrl+N for New Instance creation
- Standard Edit menu shortcuts (Undo, Redo, Cut, Copy, Paste, Select All)
- View menu shortcuts (Reload, Force Reload, Toggle DevTools, Fullscreen)
- Built-in zoom hotkeys enabled via zoomHotkeysEnabled

**Enhanced Capabilities:**
- Added core:menu:default permission for menu management
- Added core:webview:allow-set-webview-zoom for zoom functionality
- Proper event communication between Tauri backend and frontend

**Frontend Integration:**
- Tauri event listener for menu:newInstance events
- Proper cleanup and error handling for event subscriptions
- Runtime environment detection for Tauri-specific behavior

## Technical Changes

**Backend (Rust):**
- Replaced empty menu stub with full SubmenuBuilder implementation
- Added comprehensive menu event handling with window operations
- Implemented MenuItem::with_id for accelerator support
- Added platform-specific menu construction logic

**Frontend (TypeScript):**
- Added Tauri event listener integration in main App component
- Proper lifecycle management with onMount/onCleanup
- Runtime environment detection for conditional Tauri behavior

**Configuration:**
- Enabled zoomHotkeysEnabled in tauri.conf.json for built-in zoom support
- Updated capabilities to include necessary menu and webview permissions

This implementation provides a native, platform-consistent user experience with full keyboard shortcut support, matching the functionality users expect from desktop applications.

packages/tauri-app/src-tauri/tauri.conf.json

@@ -27,7 +27,8 @@
         "fullscreen": false,
         "decorations": true,
         "theme": "Dark",
-        "backgroundColor": "#1a1a1a"
+        "backgroundColor": "#1a1a1a",
+        "zoomHotkeysEnabled": true
       }
     ],
     "security": {