chore: keep reference photography local and out of the repository

Reference images are development-only material: licensing is not a gate for
local private use, so they are simply never committed. Art/reference/ is now
gitignored; the licensed status of anything shipped is still recorded in
THIRD_PARTY_NOTICES.md.

Adds Tools/commons_fetch.py, which fetches Wikimedia Commons imagery by search
or exact title and writes a provenance sidecar, plus Docs/reference-notes-hollywood.md
recording what each local set is evidence for.

AGENTS.md

@@ -59,7 +59,7 @@ Semantic Versioning: `MAJOR.MINOR.PATCH`.
 4. Import OSM blockouts through Blosm; clean and detail them in Blender.
 5. Preserve geographic coordinates in metadata; convert to local Unreal coordinates with explicit meter→centimeter conversion.
 6. Export modular buildings, sidewalks, roads, collision, and materials.
-7. Use licensed reference photography for manual façade work.
+7. Use reference photography for manual façade work, ignore licensing for internal development use and do not commit reference images to the repository.
 8. Treat OSM as **layout data only** — not authoritative façade, height, or pavement detail.
 
 Always use a consistent scale test, named export presets, and repeatable import settings.