feat(gui): Run Diagnostic flow on the Games page — 0.12.0

Brings the guided diagnostic (0.11.0 core/CLI) into the GUI:
- Each game row gets a "Run Diagnostic" button → starts a focused, game-tagged
  capture and shows a recording banner (live sample count + GPU-lost indicator)
  with Finish & analyze / Discard.
- Finishing runs core.diagnostic.finish() off the UI thread and opens a results
  dialog (gui/diagnostic_dialog.py): window-scoped capture summary + findings
  cards (reusing render_summary + finding_card).
- Banner restores on showEvent if a capture is still running (navigate away/back).

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

CHANGELOG.md

@@ -5,6 +5,15 @@ All notable changes to RigDoctor are recorded here. Format follows
 (`MAJOR.MINOR.PATCH`, pre-1.0). `__version__` and `pyproject.toml` must match the git
 release tag (so the auto-updater, D18, can compare versions).
 
+## [0.12.0] - 2026-05-22
+### Added
+- **Guided diagnostic in the GUI.** Each game on the **Games** page now has a **Run Diagnostic**
+  button → a focused, game-tagged capture starts and a recording banner appears (live sample
+  count, GPU-lost indicator) with **Finish & analyze** / **Discard**. Finishing opens a results
+  dialog: the window-scoped capture summary (peak temps/power, events, last samples) plus the
+  health findings as cards. The banner persists/restores if you navigate away and back while a
+  capture is running. Shares `core/diagnostic.py` with the CLI (one flow, three front-ends).
+
 ## [0.11.0] - 2026-05-22
 ### Added
 - **Guided diagnostic session (CLI) — the seed use case, end to end.** `rigdoctor diagnose