[KAIZEN] Implement automated burn-cycle retrospective (fixes #349)

- Add bin/kaizen-retro.sh entry point and scripts/kaizen_retro.py
- Analyze closed issues, merged PRs, and stale/max-attempts issues
- Report success rates by agent, repo, and issue type
- Generate one concrete improvement suggestion per cycle
- Post retro to Telegram and comment on the latest morning report issue
- Wire into Huey as kaizen_retro() task at 07:15 daily
- Extend gitea_client.py with since param for list_issues and
  created_at/updated_at fields on PullRequest

.gitignore

@@ -1,9 +1,8 @@
-# Secrets
-*.token
-*.key
-*.secret
-
-# Local state
+*.pyc
+*.pyo
+*.egg-info/
+dist/
+build/
 *.db
 *.db-wal
 *.db-shm