feat: Add Help menu with Check for Updates action

Menu implementation:
- Added menu bar to MainWindow
- Help menu with 'Check for Updates...' action
- Signal-based architecture for async update check
- Action triggers check_for_updates signal

Test coverage:
- 3 new tests for menu bar functionality
- Test menu bar creation
- Test signal exists and is callable
- Test callback method exists
- All 146 tests passing, 86% coverage

Design:
- Decoupled menu from update logic
- Emits signal that main app listens to
- Allows async update check without blocking UI

tests/unit/test_main_window.py

@@ -323,6 +323,38 @@ class TestMainWindowSignals:
             mock_handler.assert_called_once()
 
 
+class TestMainWindowMenuBar:
+    """Test menu bar and menu actions."""
+
+    def test_menu_bar_created(self, qtbot, sample_config):
+        """Test menu bar is created."""
+        window = MainWindow(sample_config)
+        qtbot.addWidget(window)
+        
+        menu_bar = window.menuBar()
+        assert menu_bar is not None
+
+    def test_window_has_check_for_updates_signal(self, qtbot, sample_config):
+        """Test window has check_for_updates signal."""
+        window = MainWindow(sample_config)
+        qtbot.addWidget(window)
+        
+        # Test that signal exists
+        assert hasattr(window, "check_for_updates")
+        
+        # Test that signal is callable (can be emitted)
+        assert callable(window.check_for_updates.emit)
+
+    def test_on_check_for_updates_method_exists(self, qtbot, sample_config):
+        """Test _on_check_for_updates method exists."""
+        window = MainWindow(sample_config)
+        qtbot.addWidget(window)
+        
+        # Test that the method exists
+        assert hasattr(window, "_on_check_for_updates")
+        assert callable(window._on_check_for_updates)
+
+
 class TestMainWindowStylesheet:
     """Test stylesheet application."""