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>

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "rigdoctor"
-version = "0.18.2"
+version = "0.19.0"
 description = "Modular hardware monitoring & crash diagnostics for Linux gamers."
 readme = "README.md"
 requires-python = ">=3.11"