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.

docs/blender-assets.md

@@ -5,8 +5,7 @@ Architecture context: the asset contracts and fallback path are summarized in
 
 Status: built, audited, and integrated (2026-11-01). `NpcAvatar` selects the
 character variants and attaches the gear; `WorldBuilder` loads the prop library
-with colliders and phase-driven emissives. See the Phase 3.5 integration in
-[`plan-graphics-v0.6.md`](plan-graphics-v0.6.md).
+with colliders and phase-driven emissives.
 
 Generator: [`tools/blender_assets.py`](../tools/blender_assets.py). Manifest (the
 source of truth for integration):