Repo: reclaim 8.5 GB of unreachable vendor content (audit L7/L8/M13)

Assets/ 14 GB -> 5.5 GB.

- Assets/BefourStudios DELETED (8.2 GB). Transitive-closure reachability
  from every project scene, prefab and settings asset found exactly FOUR
  reachable files in the whole pack — four textures. Relocated them to
  Assets/_Project/Textures/Env via AssetDatabase.MoveAsset with the GUIDs
  verified preserved, then removed the pack. It was HDRP art for a
  direction DR-051 deleted; re-downloadable from the Asset Store.
  (3.3 GB of that was gitignored .unitypackage archives git rm could not
  see — removed separately.)
- 92 vendor demo/gallery/overview scenes deleted (294 MB). They are the
  ten largest tracked blobs in the repo, stored as non-LFS YAML that
  Unity must parse and index on every database rebuild. Build settings
  reference only MainMenu and Game.
- com.shadercrew.the-toon-shader.3d + .core removed (132 MB embedded,
  referenced by nothing).
- Assets/Screenshots (182 PNGs, 22 MB) moved to the gitignored
  _visual_scratch/ — Unity was importing them as textures.
- manifest: dropped com.unity.ai.navigation and com.unity.cinemachine
  (zero references — no NavMesh assets, no Cinemachine in any scene).
  Pinned com.coplaydev.unity-mcp to a SHA instead of #main; that floating
  branch ref silently re-resolving IS what the dirty packages-lock.json
  was, and it means two machines can run different bridge versions while
  both match the committed manifest.

KEPT after checking, against the audit's suggestion: visualeffectgraph
(27 .vfx assets) and timeline (213 .playable) are genuinely used. And I
RESTORED com.unity.ai.assistant + com.unity.ai.inference after removing
them left half the AI Toolkit resolved in Library/PackageCache and
crashed two AssetImportWorkers on domain reload — editor-only tooling is
not worth destabilising the install for.

Verified after: 0 compile errors, 304/304 green, DevSandbox plays with
the player, an enemy, live socket stats and no leaked RPCs.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

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