Stop relying on app.openapi_schema assignment, which FastAPI 0.137.0 ignores

[gaurav]

NodeNorm is not broken today — https://nodenormalization-exp.apps.renci.org/openapi.json
(v2.5.1) still serves info.x-translator, info.x-trapi, info.contact and
info.termsOfService. This is about the trip-wire that is keeping it that way.

node_normalizer/server.py ends with

app.openapi_schema = construct_open_api_schema(app)

FastAPI stopped honouring assignment to app.openapi_schema in 0.137.0. The attribute is still
settable — /status reading app.openapi_schema["info"]["version"] keeps working — but the
/openapi.json route no longer returns it, so FastAPI serves the default document built from
FastAPI(**get_app_info()): title, description and version, and nothing else.

Bisected against a ten-line reproduction:

fastapi	info keys served
0.136.0	['title', 'version', 'x-translator']
0.137.0	['title', 'description', 'version']

The only thing standing between NodeNorm and that outcome is fastapi~=0.108.0 in
requirements.txt, which caps at <0.109. Whenever that pin moves — a security bump, a Python
upgrade, a routine dependency refresh — NodeNorm silently stops advertising the infores that
SmartAPI registration keys off, and x-trapi along with it. It fails open: the service starts,
answers queries, and serves a valid-but-wrong spec.

This is exactly what happened to NameRes, whose fastapi requirement carries no version specifier
at all: NCATSTranslator/NameResolution#294.

Suggested fix

Override the method rather than the attribute, so the pin is no longer load-bearing:

app.openapi = lambda: construct_open_api_schema(app)

Verified against fastapi 0.141.1: info.x-translator survives.

Note that construct_open_api_schema() opens with if app.openapi_schema: return app.openapi_schema() — calling a dict. It is unreachable today because the function is called
exactly once at import, but under the app.openapi = ... form it becomes reachable on the second
request. Drop it, or cache properly.

Suggested test

Nothing under tests/frontend/ covers the served spec, so this class of regression ships silently.
One in the style of tests/frontend/test_status.py:

# tests/frontend/test_openapi.py
from fastapi.testclient import TestClient
from node_normalizer.server import app


def test_openapi_json_carries_translator_metadata():
    """The served spec must carry what openapi.yml declares, not FastAPI's default document."""
    openapi = TestClient(app).get("/openapi.json").json()
    info = openapi["info"]

    assert info["x-translator"]["infores"] == "infores:sri-node-normalizer"
    assert info["x-translator"]["component"] == "Utility"
    assert info["x-trapi"]
    assert info["termsOfService"]
    assert info["contact"]
    assert openapi["servers"]

It has to go through TestClient: asserting on construct_open_api_schema(app) directly would pass
throughout the bug, since the function is fine — it is the wiring that stops being read.