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/graph/conftest.py

@@ -0,0 +1,44 @@
+"""Shared fixtures for graph tests.
+
+Provides build_mock_clients() to create ToolClients with AsyncMock fields
+so individual node functions can be tested without compiling the full graph.
+"""
+
+from unittest.mock import AsyncMock, MagicMock
+
+import pytest
+
+from release_agent.graph.dependencies import ToolClients
+
+
+def build_mock_clients() -> ToolClients:
+    """Return a ToolClients instance whose fields are all AsyncMock/MagicMock."""
+    azdo = AsyncMock()
+    jira = AsyncMock()
+    slack = AsyncMock()
+    reviewer = AsyncMock()
+    return ToolClients(azdo=azdo, jira=jira, slack=slack, reviewer=reviewer)
+
+
+def build_config(clients: ToolClients | None = None, staging_store=None) -> dict:
+    """Return a LangGraph-style config dict with clients and staging_store."""
+    if clients is None:
+        clients = build_mock_clients()
+    return {
+        "configurable": {
+            "clients": clients,
+            "staging_store": staging_store,
+        }
+    }
+
+
+@pytest.fixture()
+def mock_clients() -> ToolClients:
+    """Pytest fixture returning fresh mock ToolClients."""
+    return build_mock_clients()
+
+
+@pytest.fixture()
+def config(mock_clients: ToolClients):
+    """Pytest fixture returning a config dict with mock clients."""
+    return build_config(mock_clients)