chore: add agent credentials to gitignore (#9874)

Protect sensitive files from accidental commit:
- memory/ (moltbook credentials, session data)
- .agent/*.json (agent config, moltbook.json)

Workflows in .agent/workflows/ remain tracked.

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

.gitignore

@@ -71,3 +71,8 @@ USER.md
 
 # local tooling
 .serena/
+
+# Agent credentials and memory (NEVER COMMIT)
+memory/
+.agent/*.json
+!.agent/workflows/