fix: address PR #7 critical review issues
Address all 7 blocking issues identified in comprehensive PR review:
1. parseAtUri: Replace URL constructor with regex for at:// scheme support
2. Collection names: Use full lexicon IDs (space.atbb.forum.forum, space.atbb.forum.category)
3. Forum resolution: Add getForumIdByDid() for category/modAction records owned by Forum DID
4. ModAction subject: Access record.subject.post.uri and record.subject.did correctly
5. Circuit breaker: Track consecutive failures (max 100), stop firehose on threshold
6. Transactions: Wrap ensureUser + insert operations in db.transaction()
7. Reconnection state: Set isRunning=false on exhaustion, add health check methods
Additional improvements:
- Propagate errors from all handlers to circuit breaker
- Update test collection names and add type assertions
- Enhance error logging with event context