feat: initial commit — Billo Release Agent (LangGraph)

LangGraph-based release automation agent with:
- PR discovery (webhook + polling)
- AI code review via Claude Code CLI (subscription-based)
- Auto-create Jira tickets for PRs without ticket ID
- Jira ticket lifecycle management (code review -> staging -> done)
- CI/CD pipeline trigger, polling, and approval gates
- Slack interactive messages with approval buttons
- Per-repo semantic versioning
- PostgreSQL persistence (threads, staging, releases)
- FastAPI API (webhooks, approvals, status, manual triggers)
- Docker Compose deployment

1069 tests, 95%+ coverage.

tests/tools/fixtures/jira_issue.json

@@ -0,0 +1,10 @@
+{
+  "id": "12345",
+  "key": "ALLPOST-100",
+  "fields": {
+    "summary": "Fix the authentication bug",
+    "status": {
+      "name": "In Progress"
+    }
+  }
+}