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_diff.txt

@@ -0,0 +1,11 @@
+diff --git a/src/auth.py b/src/auth.py
+index 1234567..abcdefg 100644
+--- a/src/auth.py
++++ b/src/auth.py
+@@ -10,6 +10,10 @@ class AuthService:
+     def authenticate(self, token: str) -> bool:
+-        return token == "hardcoded"
++        return self._validate_token(token)
++
++    def _validate_token(self, token: str) -> bool:
++        return len(token) > 0 and token.startswith("Bearer ")