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_transitions.json

@@ -0,0 +1,20 @@
+{
+  "transitions": [
+    {
+      "id": "11",
+      "name": "To Do"
+    },
+    {
+      "id": "21",
+      "name": "In Progress"
+    },
+    {
+      "id": "31",
+      "name": "Done"
+    },
+    {
+      "id": "41",
+      "name": "Released"
+    }
+  ]
+}