docs(assets): per-class production briefs + template + formal deferral register (T-1049)

The asset-brief template (scope/visual-reference/naming/gen-path/
acceptance, one page) and five real briefs — station walls, rural walls,
doors, floors, furniture/props — each citing its D-235 axis tokens and
palette.md register rows (or the D-257 toon default), conventions.md
naming/mask/footprint rules, and the image-gen -> glb-gen -> promotion
path with concrete acceptance counts. Doors carry the negative
no-state-frame-files constraint (runtime mechanism stays Phase 5);
furniture/props' first acceptance is promoting the three unpromoted
spike GLBs. deferred.md is the formal register for the T-1051 four
(lamp posts, barns, TVs, billboards) + cars/Q-067, with rationale and
revisit triggers — satisfying T-1051's own 'or record formal deferral'
deliverable. Child stories under T-961 are created lead-side at merge.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/assets/README.md

@@ -26,6 +26,8 @@ docs/assets/
     audio.md             # Row template + detailed entry template for audio
     sprite.md            # LEGACY object-sprite row template (D-244 retired sprites; model/texture/artwork rows are inline in each visual/*.md file, T-1050)
     video.md             # Row template + detailed entry template for video
+    asset-brief.md       # One-page per-class brief template (scope/visual reference/naming/gen path/acceptance) — T-1049
+  briefs/                # Per-asset-class briefs gating T-961's child stories (T-1049) + deferred.md formal deferral note
   audio/
     README.md            # Audio pipeline index — categories, status summary
     palette.md           # Sonic palette, aesthetic guide, generation approach
@@ -62,3 +64,6 @@ docs/assets/
 - Decision files: `decisions/` (D-038 audio scope, D-033 entity colors, D-019 camera angle)
 - Art direction workshop: `docs/workshops/art-direction-mood-board/`
 - Sprint briefings: `docs/sprints/sprint-N/{team}.md`
+- Per-class asset briefs: [briefs/](briefs/) — station walls, rural walls, doors, floors,
+  furniture/props, each gating a T-961 child story (T-1049); [briefs/deferred.md](briefs/deferred.md)
+  records the formal deferral for lamp posts / TVs / billboards / barns (T-1051) + cars (Q-067).