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/app/flows/deploy.py

@@ -0,0 +1,60 @@
+"""Authoring pipeline: Langflow export -> versioned definition -> LFX deploy."""
+
+from __future__ import annotations
+
+from sqlmodel import Session
+
+from app.models import FlowDefinition, FlowVersion
+
+from . import store
+from .langflow_client import LangflowClient
+from .lfx_client import LfxClient
+from .schemas import FlowDefinitionCreate, FlowVersionCreate
+
+
+async def import_from_langflow(
+    session: Session,
+    langflow: LangflowClient,
+    lfx: LfxClient,
+    langflow_flow_id: str,
+    *,
+    name: str | None = None,
+    author: str = "",
+    deploy: bool = True,
+) -> tuple[FlowDefinition, FlowVersion]:
+    """Export a flow from Langflow, store it as a new version, deploy to LFX.
+
+    Definitions are matched by name (explicit `name` wins, else the exported
+    name); every import creates a new immutable version.
+    """
+    export = await langflow.export_flow(langflow_flow_id)
+    flow_name = name or export.get("name") or f"langflow-{langflow_flow_id}"
+    langflow_json = {
+        "id": export.get("id", langflow_flow_id),
+        "name": flow_name,
+        "description": export.get("description") or "",
+        "endpoint_name": export.get("endpoint_name"),
+        "data": export.get("data", {}),
+        "tags": export.get("tags", []),
+        "webhook": export.get("webhook", False),
+        "is_component": export.get("is_component", False),
+    }
+    try:
+        definition = next(
+            d for d in store.list_definitions(session) if d.name == flow_name
+        )
+    except StopIteration:
+        definition = store.create_definition(
+            session, FlowDefinitionCreate(name=flow_name)
+        )
+    version = store.create_version(
+        session,
+        definition.id,
+        FlowVersionCreate(langflow_json=langflow_json, author=author),
+    )
+    if deploy:
+        uploaded = await lfx.upload_flow(
+            version.langflow_json, flow_id=str(version.id), replace=True
+        )
+        version = store.mark_deployed(session, version, uploaded.id)
+    return definition, version