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.

.gitignore

@@ -37,5 +37,9 @@ venv/
 Thumbs.db
 *~
 
-# Environment variables
-.env
+# Credentials and environment — never committed
+.env
+*.env
+
+# Local, private reference material — never committed (see Docs/reference-notes-hollywood.md)
+/Art/reference/