chore: bootstrap repository with governance docs

Initialize git, add Apache-2.0 LICENSE, .gitattributes (LF line
endings), AGENTS.md (entry points, stack, discovery order, baseline
checks), RUNBOOK.md (dev boot, prod deploy with overlay, ingestion,
failures, rollback, scaling notes), .env.prod.example with rotated
credential placeholders, and dev-only warnings on .env.example.

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

scripts/init_opensearch.py

@@ -0,0 +1,17 @@
+"""Bootstrap the OpenSearch chunk index."""
+
+from __future__ import annotations
+
+import sys
+
+from app.indexing.opensearch_client import ensure_index
+
+
+def main() -> int:
+    ensure_index()
+    print("opensearch index ensured")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())