chore: route demo/assets GIFs through Git LFS

Track demo/assets/*.gif via Git LFS and convert the 20 existing reel GIFs
to LFS pointers. Stops binary GIF regenerations from bloating .git going
forward; existing history is left intact (no rewrite/force-push).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitattributes

@@ -0,0 +1,6 @@
+# FNXC:RepoAssets 2026-06-25-09:00:
+# Demo reel GIFs dominate repo size (the same captures get re-shot and re-committed,
+# and git keeps every old blob forever). Route them through Git LFS so the binaries
+# live outside the packfile and future regenerations stop bloating .git.
+# Scoped to demo/assets/*.gif (track-forward only — existing history was left intact).
+demo/assets/*.gif filter=lfs diff=lfs merge=lfs -text