Stage the Blender character/gear/prop library

Commit the finished generator output from the parallel Blender pass:
8 skinned NPC variants, 18 gear pieces, and 20 props under
assets/models/blender/, editable sources (gdignored), manifest, review sheets,
and the integration notes in docs/blender-assets.md.

- audit: all 46 assets clean (characters 3,788-4,640 tris, under 6000/4000)
- tests: Python manifest/audit contract and Godot import/bone/slot/ground checks
- docs: README library section, architecture/plan references, TODO Phase 3.5
  status, MEMORY integration rules
- .gitignore: per-asset preview PNGs, extracted GLB textures, blend1 backups

Nothing in the game loads the library yet; integration follows." && git log --oneline -1

.gitignore

@@ -57,3 +57,9 @@ assets/models/generated/npc_base_*_normal.png
 
 # Local AppImage extraction
 squashfs-root/
+# Blender asset library: per-asset Cycles renders are local review output (the
+# committed review artefacts are docs/blender_previews/sheet_*.jpg), and Godot
+# extracts the GLB-embedded textures next to the models on import.
+docs/blender_previews/*.png
+assets/models/blender/**/*.png
+assets/models/blender_src/*.blend1