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_alerts.py

@@ -0,0 +1,38 @@
+"""Tests for the M8 alert monitor (edge-triggered; notify mocked)."""
+
+import unittest
+from unittest import mock
+
+from rigdoctor.core import alerts
+from rigdoctor.core.sample import Reading, Sample
+
+
+def _gpu(temp):
+    return Sample(readings=[Reading("gpu", "temp", temp, "°C")])
+
+
+class AlertTests(unittest.TestCase):
+    @mock.patch.object(alerts, "notify")
+    def test_edge_triggered_no_repeat(self, m):
+        mon = alerts.AlertMonitor(gpu_temp=90.0, cooldown=0.0)
+        mon.check(_gpu(95))   # fires
+        mon.check(_gpu(96))   # still hot — no repeat while active
+        self.assertEqual(m.call_count, 1)
+        mon.check(_gpu(50))   # clears
+        mon.check(_gpu(95))   # hot again — fires
+        self.assertEqual(m.call_count, 2)
+
+    @mock.patch.object(alerts, "notify")
+    def test_no_alert_below_threshold(self, m):
+        alerts.AlertMonitor(gpu_temp=90.0).check(_gpu(70))
+        m.assert_not_called()
+
+    @mock.patch.object(alerts, "notify")
+    def test_gpu_lost(self, m):
+        mon = alerts.AlertMonitor()
+        mon.check(Sample(readings=[Reading("gpu", "status", None, "", "query-timeout")]))
+        m.assert_called_once()
+
+
+if __name__ == "__main__":
+    unittest.main()