n8n: add backend endpoints for the RAGcore Procedure Sync workflow

GET /api/v1/integrations/n8n/procedures lists every procedure Markdown
file Fleet Ops ships (all languages) with a stable per-document id and
content hash, ready for workflow 3 to push into RAGcore. POST
.../procedures-sync-result records the sync outcome as an idempotent
audit event, matching the existing return-callback/workflow-error
pattern. Extracted frontmatter parsing out of the demo knowledge
provider into a shared module so both read the same source of truth.

backend/tests/test_integrations.py

@@ -191,3 +191,69 @@ def test_workflow_error_bounds_summary_length(client):
         headers={"X-Service-Token": settings.n8n_callback_token},
     )
     assert response.status_code == 422
+
+
+def test_procedures_rejects_wrong_service_token(client):
+    response = client.get(
+        "/api/v1/integrations/n8n/procedures", headers={"X-Service-Token": "wrong-token"}
+    )
+    assert response.status_code == 401
+
+
+def test_procedures_lists_every_language_with_stable_ids(client):
+    settings = get_settings()
+    response = client.get(
+        "/api/v1/integrations/n8n/procedures",
+        headers={"X-Service-Token": settings.n8n_callback_token},
+    )
+    assert response.status_code == 200
+    documents = response.json()["documents"]
+    assert len(documents) > 0
+    assert {d["language"] for d in documents} == {"en-GB", "nl-BE", "fr-BE"}
+    checkout_docs = [d for d in documents if d["document_id"] == "vehicle-checkout-procedure"]
+    assert len(checkout_docs) == 3  # one per language
+    assert all(d["content"] and d["content_hash"] for d in checkout_docs)
+    # Same document_id, different language, must not collide on id.
+    assert len({d["id"] for d in checkout_docs}) == 3
+
+    second_response = client.get(
+        "/api/v1/integrations/n8n/procedures",
+        headers={"X-Service-Token": settings.n8n_callback_token},
+    )
+    second_ids = {d["id"] for d in second_response.json()["documents"]}
+    assert second_ids == {d["id"] for d in documents}  # ids are stable across requests
+
+
+def test_procedures_sync_result_rejects_wrong_service_token(client):
+    response = client.post(
+        "/api/v1/integrations/n8n/procedures-sync-result",
+        json={"execution_id": str(uuid.uuid4()), "synced": 5, "failed": 0},
+        headers={"X-Service-Token": "wrong-token"},
+    )
+    assert response.status_code == 401
+
+
+def test_procedures_sync_result_registers_and_is_idempotent(client, ops_client):
+    settings = get_settings()
+    headers = {"X-Service-Token": settings.n8n_callback_token}
+    execution_id = str(uuid.uuid4())
+    body = {"execution_id": execution_id, "synced": 33, "failed": 1}
+
+    first = client.post(
+        "/api/v1/integrations/n8n/procedures-sync-result", json=body, headers=headers
+    )
+    second = client.post(
+        "/api/v1/integrations/n8n/procedures-sync-result", json=body, headers=headers
+    )
+
+    assert first.status_code == 200
+    assert first.json()["status"] == "registered"
+    assert second.status_code == 200
+    assert second.json()["status"] == "already_registered"
+
+    audit_events = ops_client.get(
+        "/api/v1/audit", params={"action": "n8n_procedures_synced"}
+    ).json()
+    matching = [e for e in audit_events if e["metadata"]["execution_id"] == execution_id]
+    assert len(matching) == 1
+    assert matching[0]["after"] == {"synced": 33, "failed": 1}