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>

docs/ROADMAP.md

@@ -30,8 +30,10 @@ Ubuntu + NVIDIA first; `.deb` distribution (see `DECISIONS.md`).
 - [~] M6 gaming environment checks (suggest-only) — *Steam game/library detection done*
       (multi-library `libraryfolders.vdf` discovery + `appmanifest` scan, opt-in libraries,
       launch-time background rescan with new-game badge; CLI `rigdoctor games`, GUI Games page).
-      This is also the D12 "pick a game" foundation. *Pending:* the env-check probes (governor,
-      GPU persistence, GameMode/MangoHud, swappiness, hugepages, mitigations, PCIe ASPM).
+      This is also the D12 "pick a game" foundation. *Env-check engine done* (`rigdoctor gameenv`
+      + GUI Environment page): PCIe ASPM, NVIDIA persistence, CPU governor, GameMode, MangoHud,
+      swappiness, shader cache, THP, mitigations, Proton versions — read-only with fix commands.
+      *Pending:* non-Steam launchers (Lutris/Heroic) + GPU power-profile (PowerMizer) checks.
 - [ ] SMART integration (smartmontools if present)
 
 ## Phase 4 — Desktop UI & installer