The handoff stays on disk, not in the repo

The prototype ships a copy of thirty repo assets and the zip is a second copy
again — a megabyte of duplicate art in the history for a document whose
decisions now live in PROJECT.md and in the code. The folder is ignored, not
deleted: it is still there to read.

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

.gitignore

@@ -13,3 +13,8 @@ promo/clips/
 # ios/.gitignore already keeps the copied web payload, Pods and Xcode's per-user junk out of it.
 node_modules/
 www/
+
+# design hand-offs: read, built, and recorded in PROJECT.md — the prototype, its copy of the
+# assets and the zip do not belong in the image or the history (they are ~1 MB of duplicate art)
+design_handoff_*/
+*.zip