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>

docs/MODULES.md

@@ -12,7 +12,7 @@ Status: ⬜ not started · 🟦 designing · 🟨 in progress · ✅ done
 | M3 | Crash-capture logger | Essential | none (opt: smartmontools) | all (NVIDIA first) | P0 | 🟨 |
 | M4 | Health report (log scan) | Essential | none (opt: smartmontools) | all (NVIDIA first) | P0 | 🟨 |
 | M2 | Live monitor (TUI) | Monitoring | none (stdlib curses) | all | P1 | ⬜ |
-| M8 | Alerting | Monitoring | libnotify (opt) | all | P2 | ⬜ |
+| M8 | Alerting | Monitoring | libnotify (opt) | all | P2 | 🟨 |
 | M5 | System inventory | Diagnostics | none (opt: lm-sensors, dmidecode) | all | P1 | 🟨 |
 | M6 | Gaming env checks | Diagnostics | none | all | P2 | ⬜ |
 | M10 | Desktop GUI | Desktop UI | **python3-pyside6** | all | P2 | 🟨 |