feat(gui): explain Run Diagnostic + offer to launch the game — 0.13.0

The recording banner gave no guidance, so it wasn't clear what to do after
clicking Run Diagnostic.

- Start dialog now spells out the flow: play the game, reproduce the crash, then
  Finish & analyze (data survives a hard freeze + reboot), with "Launch game &
  start" (steam.launch_game via steam:// appid URL) or "Start without launching".
- Recording banner now states the next step, not just a sample count.
- steam.launch_game(appid): best-effort Steam launch (steam / xdg-open).
- Fix: escape "&" in button labels (Qt mnemonic) so "Finish & analyze" shows
  correctly instead of "Finish _analyze".

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 = "0.12.0"
+version = "0.13.0"
 description = "Modular hardware monitoring & crash diagnostics for Linux gamers."
 readme = "README.md"
 requires-python = ">=3.11"