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/azdo_pr.json

@@ -0,0 +1,16 @@
+{
+  "pullRequestId": 42,
+  "title": "Fix the auth bug",
+  "status": "active",
+  "sourceRefName": "refs/heads/bug/ALLPOST-999_fix-auth",
+  "targetRefName": "refs/heads/main",
+  "url": "https://dev.azure.com/my-org/my-project/_apis/git/repositories/my-repo/pullRequests/42",
+  "repository": {
+    "id": "repo-uuid-123",
+    "name": "my-repo",
+    "remoteUrl": "https://dev.azure.com/my-org/my-project/_git/my-repo"
+  },
+  "lastMergeSourceCommit": {
+    "commitId": "abc123def456"
+  }
+}