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_langflow_client.py

@@ -0,0 +1,52 @@
+"""LangflowClient HTTP mapping tests (Langflow mocked via respx, no LFX)."""
+
+import httpx
+import pytest
+import respx
+
+from app.flows.langflow_client import (
+    LangflowClient,
+    LangflowNotFound,
+    LangflowUnavailable,
+)
+
+BASE = "https://langflow.test"
+
+
+def _client():
+    return LangflowClient(BASE, api_key="test-key")
+
+
+@respx.mock
+async def test_export_flow_sends_api_key_and_returns_doc():
+    doc = {"id": "abc", "name": "n", "data": {"nodes": [], "edges": []}}
+    route = respx.get(f"{BASE}/api/v1/flows/abc").mock(
+        return_value=httpx.Response(200, json=doc)
+    )
+    result = await _client().export_flow("abc")
+    assert result == doc
+    assert route.called
+    assert route.calls[0].request.headers["x-api-key"] == "test-key"
+
+
+@respx.mock
+async def test_export_flow_not_found():
+    respx.get(f"{BASE}/api/v1/flows/missing").mock(
+        return_value=httpx.Response(404, json={"detail": "nope"})
+    )
+    with pytest.raises(LangflowNotFound):
+        await _client().export_flow("missing")
+
+
+@respx.mock
+async def test_list_flows_unwraps_items():
+    respx.get(f"{BASE}/api/v1/flows/").mock(
+        return_value=httpx.Response(200, json={"items": [{"id": "1"}]})
+    )
+    assert await _client().list_flows() == [{"id": "1"}]
+
+
+async def test_unreachable_raises_unavailable():
+    client = LangflowClient("https://langflow.dead", api_key="k")
+    with pytest.raises(LangflowUnavailable):
+        await client.export_flow("whatever")