feat: Steam game & library detection (M6) — 0.8.0

The first slice of M6 (gaming-environment checks): detect a user's Steam
libraries and the games installed in each — also the D12 "pick a game"
foundation.

- core/steam.py: multi-install/library discovery (libraryfolders.vdf, symlink
  dedupe, native/Flatpak/Snap), appmanifest_*.acf scan with runtime/Proton/
  redist filtering, scan cache + new-game diff. Stdlib only. VDF keys read
  case-insensitively (e.g. lastupdated vs SizeOnDisk).
- Libraries are opt-in (config steam_libraries); the flat TOML writer now
  emits list/array values.
- GUI Games page: library checkboxes with per-library counts, game list,
  background rescan on every launch, NEW badge + sidebar count for games
  installed since the last scan (acknowledged when viewed).
- CLI: rigdoctor games / games libraries [--enable|--disable|--all|--json]
  (headless-complete, D17).
- Tests for VDF parse, scan, tool filter, cache diff, config list round-trip.
- Docs (MODULES/ROADMAP) updated; version 0.7.3 -> 0.8.0.

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 = "0.7.3"
+version = "0.8.0"
 description = "Modular hardware monitoring & crash diagnostics for Linux gamers."
 readme = "README.md"
 requires-python = ">=3.11"