fix: address CodeRabbit review issues for PR #113

- Add ESCAPE clause to LIKE query for proper wildcard escaping
- Normalize timestamps with "Z" suffix in get_agent_stats()
- Add cleanup interval (100 inserts) to avoid cleanup on every insert
- Use context managers for DB connections in LogQuery methods
- Move import shutil to module level in tests
- Use assertEqual instead of assertLessEqual for max_entries test
- Fix test_log_warn to query for "warn" (normalized level)

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

Author: cabana8471-arch