v0.11.1 — OpenAPI schema fix for the trace export route

Patch release. The trace router's /api/traces/export handler broke OpenAPI
schema generation — its -> JSONResponse return annotation is an unresolvable
forward ref, so /openapi.json and /docs raised PydanticUserError. The
route now declares response_model=None. No behavior change.

Fixed

• The trace router's /api/traces/export handler broke OpenAPI schema
  generation: its -> JSONResponse return annotation is an unresolvable forward
  ref (the module uses from __future__ import annotations and imports fastapi
  lazily inside create_trace_router), so /openapi.json and /docs raised
  PydanticUserError. The route now declares response_model=None.