refactor(gui): grouped navigation + clearer page names — 0.20.0

Reshape the IA so it reads by intent instead of a flat pile of pages.

- Grouped sidebar: Monitor / Diagnose / System / App (section headers).
- Renames: Health → System Health, Environment → Tuning, Logs → Recordings,
  Setup → Settings.
- Settings absorbs Notifications (alerts) as a section; Notifications dropped as a
  separate page (notifications_page.py removed; SetupPage gains the alerts card +
  `changed` signal wired to the live alert monitor).
- Recordings is now a hub: a source dropdown to view any captured log (always-on /
  last diagnostic / preserved crash) + Analyze-crash in place, plus the recorder
  controls; status line now shows the captured game.
- main_window nav is data-driven (_NAV groups → _PAGES order → stack); show_page,
  badges, and tray flows updated. GUI smoke test asserts the new page set.

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

tests/test_gui_smoke.py

@@ -36,7 +36,8 @@ class GuiSmokeTests(unittest.TestCase):
              mock.patch.object(updates, "update_state", return_value=(updates.UP_TO_DATE, None, "")):
             window = mw.MainWindow()
         try:
-            self.assertEqual(len(window._nav_buttons), len(mw._NAV_ITEMS))
+            self.assertEqual(len(window._nav_buttons), len(mw._PAGES))
+            self.assertEqual(set(window._nav_buttons), set(mw._PAGES))
         finally:
             window._worker.stop()