Security: Add .gitignore, remove sensitive files from tracking

- Added comprehensive .gitignore for secrets, tokens, session data
- Untracked openclaw.json (contains API tokens)
- Untracked device-auth.json, paired.json
- Untracked session .jsonl files (conversation history)
- Untracked cron run logs

Note: Files still exist locally, just no longer version controlled

agents/main/sessions/bd8ce668-8db7-49eb-8dfa-67aac370286a.jsonl.lock

@@ -1,4 +0,0 @@
-{
-  "pid": 20989,
-  "createdAt": "2026-02-05T17:29:15.892Z"
-}