feat: Add status bar with update status indicator

Status bar implementation:
- Status bar at bottom of main window
- Update status label with emoji support
- set_update_status() method for updates:
  -  Checking for updates
  -  Update available
  -  Downloading update
  -  Update failed
  - Clean status display

Test coverage:
- 8 new tests for status bar
- Test creation and initialization
- Test status updates with/without emoji
- Test all status states (checking, available, downloading, error)
- All 154 tests passing, 86% coverage

Enables visual feedback during update operations

tests/unit/test_main_window.py

@@ -355,6 +355,75 @@ class TestMainWindowMenuBar:
         assert callable(window._on_check_for_updates)
 
 
+class TestMainWindowStatusBar:
+    """Test status bar and update status."""
+
+    def test_status_bar_created(self, qtbot, sample_config):
+        """Test status bar is created."""
+        window = MainWindow(sample_config)
+        qtbot.addWidget(window)
+        
+        assert window.statusBar() is not None
+        assert hasattr(window, "status_bar")
+
+    def test_update_status_label_created(self, qtbot, sample_config):
+        """Test update status label exists."""
+        window = MainWindow(sample_config)
+        qtbot.addWidget(window)
+        
+        assert hasattr(window, "update_status_label")
+        assert window.update_status_label is not None
+
+    def test_set_update_status_text_only(self, qtbot, sample_config):
+        """Test setting update status with text only."""
+        window = MainWindow(sample_config)
+        qtbot.addWidget(window)
+        
+        window.set_update_status("Checking for updates")
+        assert "Checking for updates" in window.update_status_label.text()
+
+    def test_set_update_status_with_emoji(self, qtbot, sample_config):
+        """Test setting update status with emoji."""
+        window = MainWindow(sample_config)
+        qtbot.addWidget(window)
+        
+        window.set_update_status("Checking", emoji="🔄")
+        assert "🔄" in window.update_status_label.text()
+        assert "Checking" in window.update_status_label.text()
+
+    def test_set_update_status_checking(self, qtbot, sample_config):
+        """Test checking for updates status."""
+        window = MainWindow(sample_config)
+        qtbot.addWidget(window)
+        
+        window.set_update_status("Checking for updates", emoji="🔄")
+        assert "🔄" in window.update_status_label.text()
+
+    def test_set_update_status_available(self, qtbot, sample_config):
+        """Test update available status."""
+        window = MainWindow(sample_config)
+        qtbot.addWidget(window)
+        
+        window.set_update_status("Update available v0.0.2", emoji="✅")
+        assert "✅" in window.update_status_label.text()
+
+    def test_set_update_status_downloading(self, qtbot, sample_config):
+        """Test downloading status."""
+        window = MainWindow(sample_config)
+        qtbot.addWidget(window)
+        
+        window.set_update_status("Downloading update", emoji="⬇️")
+        assert "⬇️" in window.update_status_label.text()
+
+    def test_set_update_status_error(self, qtbot, sample_config):
+        """Test error status."""
+        window = MainWindow(sample_config)
+        qtbot.addWidget(window)
+        
+        window.set_update_status("Update check failed", emoji="⚠️")
+        assert "⚠️" in window.update_status_label.text()
+
+
 class TestMainWindowStylesheet:
     """Test stylesheet application."""