feat: Langflow authoring pipeline with tests

- LangflowClient (list/export, x-api-key auth, error mapping)
- import_from_langflow: export -> versioned definition -> LFX deploy
- POST /api/flows/import, GET /api/flows/langflow/available
- scripts/deploy_flow.py CLI
- 25 tests green (Langflow faked via dependency override + respx
  client tests; respx passthrough proven unreliable for LFX traffic)

backend/tests/test_deploy.py

@@ -0,0 +1,109 @@
+"""Step 4 tests: Langflow import pipeline (Langflow faked, LFX real)."""
+
+import json
+from pathlib import Path
+from uuid import uuid4
+
+FIXTURES = Path(__file__).parent / "fixtures" / "flows"
+LANGFLOW_ID = "11111111-2222-4333-8444-555555555555"
+
+
+def _export_doc(name="importiert"):
+    fixture = json.loads((FIXTURES / "simple_rule.json").read_text())
+    return {
+        "id": LANGFLOW_ID,
+        "name": name,
+        "description": "aus Langflow",
+        "endpoint_name": None,
+        "data": fixture["data"],
+        "tags": [],
+        "webhook": False,
+        "is_component": False,
+    }
+
+
+async def test_import_creates_definition_version_and_deploys(
+    client, lfx_server, override_langflow
+):
+    override_langflow(_export_doc())
+    response = await client.post(
+        "/api/flows/import",
+        json={"langflow_flow_id": LANGFLOW_ID, "author": "admin"},
+    )
+    assert response.status_code == 201, response.text
+    body = response.json()
+    assert body["definition"]["name"] == "importiert"
+    assert body["version"]["version_no"] == 1
+    assert body["version"]["author"] == "admin"
+    assert body["version"]["lfx_flow_id"] == body["version"]["id"]
+    assert body["version"]["deployed_at"] is not None
+    assert body["version"]["langflow_json"]["data"]["nodes"]
+
+    # Imported flow actually runs on LFX.
+    definition_id = body["definition"]["id"]
+    response = await client.post(
+        f"/api/flows/{definition_id}/run", json={"input": {"betrag": 10}}
+    )
+    assert response.status_code == 200, response.text
+    assert response.json()["status"] == "completed"
+
+
+async def test_import_reuses_definition_and_bumps_version(
+    client, lfx_server, override_langflow
+):
+    override_langflow(_export_doc())
+    first = await client.post(
+        "/api/flows/import", json={"langflow_flow_id": LANGFLOW_ID}
+    )
+    second = await client.post(
+        "/api/flows/import", json={"langflow_flow_id": LANGFLOW_ID}
+    )
+    assert first.status_code == 201
+    assert second.status_code == 201
+    assert first.json()["definition"]["id"] == second.json()["definition"]["id"]
+    assert second.json()["version"]["version_no"] == 2
+
+
+async def test_import_with_explicit_name(client, lfx_server, override_langflow):
+    override_langflow(_export_doc(name="langflow-name"))
+    response = await client.post(
+        "/api/flows/import",
+        json={"langflow_flow_id": LANGFLOW_ID, "name": "wunschname"},
+    )
+    assert response.status_code == 201, response.text
+    assert response.json()["definition"]["name"] == "wunschname"
+
+
+async def test_import_without_deploy(client, override_langflow):
+    override_langflow(_export_doc())
+    response = await client.post(
+        "/api/flows/import",
+        json={"langflow_flow_id": LANGFLOW_ID, "deploy": False},
+    )
+    assert response.status_code == 201, response.text
+    body = response.json()
+    assert body["version"]["lfx_flow_id"] is None
+    assert body["version"]["deployed_at"] is None
+
+
+async def test_import_langflow_not_found(client, override_langflow):
+    override_langflow(status=404)
+    response = await client.post(
+        "/api/flows/import", json={"langflow_flow_id": LANGFLOW_ID}
+    )
+    assert response.status_code == 404
+
+
+async def test_import_langflow_unreachable(client, override_langflow):
+    override_langflow(status=0)
+    response = await client.post(
+        "/api/flows/import", json={"langflow_flow_id": str(uuid4())}
+    )
+    assert response.status_code == 503
+
+
+async def test_list_langflow_flows(client, override_langflow):
+    override_langflow(_export_doc())
+    response = await client.get("/api/flows/langflow/available")
+    assert response.status_code == 200
+    assert response.json() == [{"id": "fake-1", "name": "fake"}]