feat: integrate Analyst into Plane/Orchestrator pipeline

- Add git fetch+checkout in agent launch cmd (ensures correct branch)
- Add git fetch+checkout in _monitor_agent before commit/push
- Post start comment in Plane when analyst launches
- Post :approved: request comment after analyst completes successfully
- Branch lookup moved before cmd construction for reuse

tests/test_webhooks.py

@@ -6,6 +6,8 @@ from unittest.mock import patch, MagicMock, AsyncMock
 # Override DB path before importing app
 _test_db = os.path.join(tempfile.gettempdir(), "test_orchestrator.db")
 os.environ["ORCH_DB_PATH"] = _test_db
+os.environ["ORCH_PLANE_WEBHOOK_SECRET"] = ""
+os.environ["ORCH_GITEA_WEBHOOK_SECRET"] = ""
 os.environ["ORCH_REPOS_DIR"] = tempfile.gettempdir()
 os.environ["ORCH_HOST_REPOS_DIR"] = "/home/slin/repos"
 os.environ["ORCH_GITEA_TOKEN"] = "test-token"