feat(gui): system-tray applet (M11) + GUI smoke tests — 0.19.0

QSystemTrayIcon applet (gui/tray.py, D13): menu with live CPU/GPU temp + memory
used/total, a status line, a Run Diagnostic submenu per detected game, plus Open
dashboard / Start-Stop recording / Snapshot-copy / Quit. Reuses the dashboard's
sample stream; drives existing MainWindow flows.

- MainWindow creates the tray when one is available; closing the window hides to
  tray (Quit exits); setQuitOnLastWindowClosed(False) so dialogs don't quit it.
- app: `--tray` starts hidden for autostart.
- tests/test_gui_smoke.py: construct MainWindow headless + exercise the tray, so
  a startup crash (like the 0.18.0 import bug) fails the build. Skips if no PySide6.
- docs: M10/M11 marked done in MODULES/ROADMAP.

Completes the Desktop UI bundle (M10 + M11).

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

tests/test_gui_smoke.py

@@ -0,0 +1,68 @@
+"""GUI smoke tests: construct the real widgets so a startup crash fails the build.
+
+These run headless (offscreen) and skip cleanly if PySide6 isn't installed (the core/CLI
+test suite stays Qt-free). Constructing MainWindow is the check that would have caught the
+0.18.0 bad-import regression that broke launch.
+"""
+
+import os
+import time
+import unittest
+
+os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
+
+try:
+    from PySide6.QtGui import QIcon
+    from PySide6.QtWidgets import QApplication, QWidget
+    HAVE_QT = True
+except ImportError:
+    HAVE_QT = False
+
+
+@unittest.skipUnless(HAVE_QT, "PySide6 not installed")
+class GuiSmokeTests(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        cls.app = QApplication.instance() or QApplication([])
+
+    def test_main_window_constructs(self):
+        from unittest import mock
+
+        from rigdoctor.core import updates
+        from rigdoctor.gui import main_window as mw
+
+        # Avoid construction side effects: no pkexec elevation, no network update check.
+        with mock.patch("rigdoctor.core.elevation.available", return_value=False), \
+             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))
+        finally:
+            window._worker.stop()
+
+    def test_tray_readouts_update(self):
+        from rigdoctor.core.sample import Reading, Sample
+        from rigdoctor.gui.tray import TrayIcon
+
+        class StubWindow(QWidget):
+            def show_dashboard(self): ...
+            def show_page(self, name): ...
+            def run_diagnostic(self, name, appid): ...
+            def quit_app(self): ...
+
+        tray = TrayIcon(StubWindow(), QIcon())
+        tray.update_sample(Sample(time.time(), [
+            Reading("gpu", "temp", 72.0, "°C", ""),
+            Reading("cpu", "temp", 65.0, "°C", "Package id 0"),
+            Reading("memory", "used", 14.2, "GB"),
+            Reading("memory", "total", 31.0, "GB"),
+            Reading("memory", "used_pct", 46.0, "%"),
+        ]))
+        self.assertIn("72", tray._gpu_act.text())
+        self.assertIn("65", tray._cpu_act.text())
+        self.assertIn("14.2 / 31.0 GB", tray._mem_act.text())
+        self.assertEqual(tray._status_act.text(), "● Normal")
+
+
+if __name__ == "__main__":
+    unittest.main()