Remove the obsolete graphics plan

Delete docs/plan-graphics-v0.6.md and update README, architecture, asset
tooling, Blender docs and MEMORY references. Completed work stays summarized
in ADR-0013, the asset-pipeline architecture and the changelog; the v1.0.0
roadmap owns future graphics work.

README.md

@@ -115,7 +115,6 @@ Full setup, every run/test/smoke command, and the controls table are in
 - [`docs/blender-assets.md`](docs/blender-assets.md) — Blender asset library: characters, gear, props, attach points.
 - [`docs/adr/`](docs/adr/) — Architecture Decision Records.
 - [`TODO.md`](TODO.md) — Active tasks plus the v1.0.0 gap analysis and milestone roadmap.
-- [`docs/plan-graphics-v0.6.md`](docs/plan-graphics-v0.6.md) — Historical v0.6 graphics program (completed).
 
 ## Development Status