chore(gitignore): exclude MM-Fi dataset archives (assets/MM-Fi/*.zip)

The MM-Fi benchmark environment archives (E01-E04.zip) are large data
files fetched separately for evaluation — they must never be committed.
Also keeps the existing aether-arena/staging/ private-staging exclusion.

Co-Authored-By: claude-flow <ruv@ruv.net>

Author: ruvnet

.gitignore

@@ -261,3 +261,10 @@ v2/crates/rvcsi-node/*.node
 v2/crates/rvcsi-node/binding.js
 v2/crates/rvcsi-node/binding.d.ts
 v2/crates/rvcsi-node/npm/
+
+# AetherArena private optimization staging — never published until reviewed
+aether-arena/staging/
+
+# MM-Fi benchmark dataset archives — large data, fetch separately, never commit
+assets/MM-Fi/E0*.zip
+assets/MM-Fi/*.zip