feat: gaming environment checks engine (M6) + notification icon — 0.9.0

The evaluate-and-suggest half of M6: a read-only findings report (D9) over
system settings that affect gaming stability/performance, each with the exact
fix command.

- core/gameenv.py: PCIe ASPM, NVIDIA persistence mode, CPU governor (the three
  seed-case contributors to GPU bus-drop / Xid 79), GameMode, MangoHud,
  vm.swappiness, shader disk cache, THP, CPU mitigations, Proton versions.
  Pure evaluate_* helpers split from IO for testing; reuses the M4 Finding model.
- steam.proton_versions(): surfaces installed Proton builds for the report.
- CLI: rigdoctor gameenv (text / --json); render_health() gained a title arg.
- GUI: new Environment page; extracted a shared finding_card widget and switched
  the Health page to it.
- Tests for the pure evaluators + aggregate.

Also fix: desktop notifications now use the RigDoctor icon (installed theme copy
-> bundled asset -> stock fallback) instead of a generic stock icon, matching
the app/dock icon.

Docs (MODULES/ROADMAP) updated; version 0.8.0 -> 0.9.0.

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

CHANGELOG.md

@@ -5,6 +5,20 @@ 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).
 
+## [0.9.0] - 2026-05-22
+### Added
+- **Gaming environment checks (M6) — the evaluate-and-suggest engine.** A new read-only report
+  (D9) that flags system settings which hurt gaming stability/performance and gives the exact fix
+  command. Checks: **PCIe ASPM**, **NVIDIA persistence mode**, **CPU governor** (the three that
+  map to the seed-case GPU bus-drop / Xid 79), GameMode, MangoHud, `vm.swappiness`, shader disk
+  cache, Transparent HugePages, CPU mitigations, and installed Proton versions.
+  - **CLI:** `rigdoctor gameenv` (text or `--json`).
+  - **GUI:** a new **Environment** page (findings cards, auto-runs on open), reusing the M4
+    health-report card style via a shared `finding_card` widget.
+### Fixed
+- **Notification icon** now uses the RigDoctor icon (matching the app/dock) instead of a generic
+  stock icon — resolved from the installed icon theme, the bundled asset, then a stock fallback.
+
 ## [0.8.0] - 2026-05-22
 ### Added
 - **Gaming environment checks (M6) — Steam game detection.** RigDoctor now finds your Steam