chore: gitignore launch materials

Keep marketing docs local-only, not in public repo.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: TC407-api

.gitignore

@@ -39,3 +39,6 @@ build/
 # Logs
 *.log
 logs/
+
+# Marketing/Launch materials (keep local only)
+launch/