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.

TODO.md

@@ -18,10 +18,10 @@ strong vertical slice, not yet a 1.0 product.
 - [x] Keep command-heavy operational pages separate but subordinate: `docs/asset-tooling.md`,
       `docs/blender-assets.md`, `docs/getting-started.md`, `docs/RELEASING.md` and
       `docs/smoke-checklist.md` now link to architecture rather than acting as parallel sources.
-- [x] Mark `docs/plan-graphics-v0.6.md` as completed/historical; current graphics work belongs in
-      this roadmap.
+- [x] Remove the obsolete `docs/plan-graphics-v0.6.md` and its links; completed graphics work is
+      represented by ADR-0013, the asset pipeline section and the changelog.
 - [x] Resolve stale claims: README release version/download row, development status
-      "Forward+ not implemented", Blender props "not AO-baked", and historical plan status.
+      "Forward+ not implemented", and Blender props "not AO-baked".
 - [x] Record the documentation ownership rule in `docs/architecture.md` §12: design intent
       (`PLAN.md`), mechanics (`gameplay.md`), system architecture/contracts (`architecture.md`),
       decisions (ADRs), status (`development-status.md`), roadmap (`TODO.md`), operations