gitignore data/ for global AGENTS.md

The /data dir is host-mounted into the container at /data:ro and holds
the global AGENTS.md seed (v1.8.1). It is part of the deployment
contract — anyone cloning needs to mkdir data/ + cp AGENTS.md into it
themselves — so the directory itself should never be tracked.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -6,3 +6,4 @@ dist
 .vite
 coverage
 secrets/
+data/