chore: make the Blender files writable and commit the regenerated asset state

Every .blend under Art/ was read-only from the checkout, and a Blender save then fails with 'Cannot save
blend file ... is not writable'. In Tools/hero_facade_build.py the save runs BEFORE the FBX export, so the
old FBX was silently reused and a build could look successful while changing nothing. All 20 .blend and
.blend1 files are now writable and 'find Art -name *.blend ! -perm -u+w' returns nothing.

Re-rendered the full capture set afterwards. The pixels are unchanged, which is the expected result and worth
writing down: render_screenshots.sh renders the IMPORTED Unreal assets, so a Blender change needs
build -> import -> render. Chmod alone cannot change an image.

Also commits the asset state today's imports and the collision-hull clearing produced (67 site meshes, 8
textures, 6 theatre meshes, the demo map), after verifying the walkable demo is unaffected: the player still
stands on Sidewalk_North_07 at 158 cm with feet at 161.

MEMORY.md

@@ -594,3 +594,8 @@ Road_Hollywood_07 158   (was 366)
 
 - **Two things had to change together:** the road had to be exported in slices, _and_ the map had to stop staging the single `Road_Hollywood` asset, which still sat on top of the slices and won every trace.
 - General lesson: a long walkable mesh needs slicing in the source, because Unreal's simple collision is a convex hull of the whole mesh - the per-slice hull is the only way its collision follows its surface.
+
+## 2026-11-10 — `chmod u+w` on the Blender files, and what re-rendering does not do
+
+- Every `.blend` under `Art/` checked out read-only; a Blender save then fails with `RuntimeError: Error: Cannot save blend file ... is not writable`, and because the export happens after the save in `Tools/hero_facade_build.py`, **the FBX is never written and the old one is reused silently**. All 20 `.blend`/`.blend1` files were made writable; `find Art -name '*.blend' ! -perm -u+w` now returns 0.
+- **Re-rendering does not pick up `.blend` changes.** `Tools/render_screenshots.sh` renders the imported UE assets, so a rebuild is needed in between: Blender build → `Tools/ue_*_import.py` → render. Chmod alone cannot change a pixel; the hero captures are byte-identical before and after.