feat: alerts (M8), notifications config page, and app icon (0.4.0)

- feat(alerts): desktop notifications (notify-send) for overheat (GPU/CPU past a
  configurable threshold), GPU-lost, and a new-version-available alert (once per
  version). Edge-triggered with cooldown so it doesn't spam (core/alerts.py)
- feat(gui): Notifications page to configure alerts (enable, GPU/CPU thresholds,
  Send test); changes apply live and persist via config.save_config/update_config
- feat(gui): ship a RigDoctor icon; the GUI self-registers the icon + .desktop on
  launch and sets the Wayland app-id, so the dock shows it after an update + relaunch
  (no installer re-run); installer/uninstaller updated to manage the icon
- config: alerts_enabled, gpu_temp_alert, cpu_temp_alert; flat-TOML writer
- tests for the alert monitor and config round-trip

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_config.py

@@ -0,0 +1,32 @@
+"""Tests for config save/load (flat TOML writer)."""
+
+import tempfile
+import unittest
+from pathlib import Path
+from unittest import mock
+
+from rigdoctor import config
+
+
+class ConfigTests(unittest.TestCase):
+    def test_save_load_round_trip(self):
+        with tempfile.TemporaryDirectory() as d:
+            cf = Path(d) / "config.toml"
+            with mock.patch.object(config, "CONFIG_FILE", cf), mock.patch.object(config, "CONFIG_DIR", Path(d)):
+                config.save_config({"alerts_enabled": False, "gpu_temp_alert": 88.0, "update_check_minutes": 5})
+                loaded = config.load_config()
+                self.assertIs(loaded["alerts_enabled"], False)
+                self.assertEqual(loaded["gpu_temp_alert"], 88.0)
+                self.assertEqual(loaded["update_check_minutes"], 5)
+
+    def test_update_config_merges_and_keeps_defaults(self):
+        with tempfile.TemporaryDirectory() as d:
+            cf = Path(d) / "config.toml"
+            with mock.patch.object(config, "CONFIG_FILE", cf), mock.patch.object(config, "CONFIG_DIR", Path(d)):
+                config.update_config(cpu_temp_alert=70.0)
+                self.assertEqual(config.load_config()["cpu_temp_alert"], 70.0)
+                self.assertEqual(config.load_config()["gpu_temp_alert"], 90.0)  # default preserved
+
+
+if __name__ == "__main__":
+    unittest.main()