Add project infrastructure and core application files

Add .gitignore, GitLab CI pipeline with test/lint/build/release stages, project documentation (README, LICENSE, CHANGELOG, CONTRIBUTING, SECURITY), PyInstaller packaging configuration with icon and version info, Python project configuration with dependencies, and complete application source including battery provider, device discovery, settings management, UI components, startup control, and comprehensive test suite

tests/test_mock_provider.py

@@ -0,0 +1,25 @@
+from datetime import datetime
+
+import pytest
+
+from logitech_battery_widget.battery.mock_provider import MockBatteryProvider
+from logitech_battery_widget.battery.provider import BatteryDevice, ChargeStatus
+
+
+def test_mock_provider_returns_multiple_independent_devices():
+    first = MockBatteryProvider().get_devices()
+    second = MockBatteryProvider().get_devices()
+
+    assert len(first) == 2
+    assert all(device.updated_at is not None for device in first)
+    assert first is not second
+
+
+def test_custom_mock_devices_are_preserved():
+    device = BatteryDevice("id", "Test", 42, ChargeStatus.CHARGING, datetime.now())
+    assert MockBatteryProvider([device]).get_devices() == [device]
+
+
+def test_invalid_percentage_is_rejected():
+    with pytest.raises(ValueError):
+        BatteryDevice("id", "Test", 101)