docs(assets): 3D-model+texture catalog, glb-gen production path, conventions (T-1050)

Instantiates the five D-244 catalog files (models/textures/artwork/icons/
effects — icons carries the 13 as-built SVGs, stance icons traced to their
consumer and marked final), creates client/assets/models/{furniture,props}
with a schema-documented manifest.json mirroring the character manifest,
fixes glb-gen SKILL.md's stale 'path does not exist' paragraph, and authors
docs/assets/visual/conventions.md: category-first model naming (araminta
ruling), mask sidecars per the character convention, D-235-token-keyed
texture naming, footprint_tiles as manifest metadata. Door-state and
TileSet conventions are recorded as explicit deferrals (Phase-5 owned).
visual/README.md carries both this ticket's count/link updates and
T-1052's palette-section rewrite (shared file, committed here).

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

docs/assets/README.md

@@ -24,7 +24,7 @@ docs/assets/
   README.md              # This file — master index
   _templates/
     audio.md             # Row template + detailed entry template for audio
-    sprite.md            # LEGACY object-sprite row template (D-244 retired sprites; model/texture/artwork template TBD)
+    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
   audio/
     README.md            # Audio pipeline index — categories, status summary
@@ -40,6 +40,7 @@ docs/assets/
     artwork.md           # Flat 2D art — paintings, flags, billboards, signage (via /sprite-gen)
     icons.md             # UI icons, status indicators (UI layer)
     effects.md           # Shaders, particles, overlays
+    conventions.md       # Model naming, mask sidecars, D-235-keyed texture naming, footprint metadata (T-1050)
   video/
     README.md            # Video pipeline index
     palette.md           # Motion/editing style guide