fix(test-schemathesis): disable rate limiter in fuzz subprocess

Schemathesis fires up to 3000 examples per endpoint. POST /auth/login
caps at 10/5min per IP, so the second example onward returns 429 and
the positive_data_acceptance check flags it as RejectedPositiveData
(its allowed-status list is hardcoded in schemathesis to
2xx/401/403/404/409/5xx, so OpenAPI tweaks can't fix it).

DECNET_LIMITER_ENABLED=false exists for exactly this case (see
limiter.py docstring on stress/load testing).

Reverts the custom_openapi shim from 5d88346 / 9b1168c — the endpoint
already declares 429 in its responses= map (api_login.py:38), and the
shim turned out to address a problem that wasn't there. Drop the
companion test along with it.

tests/web/test_openapi_rate_limit.py

@@ -1,50 +0,0 @@
-"""OpenAPI must advertise 429 on every slowapi-rate-limited operation.
-
-Other endpoints may also advertise 429 for their own reasons (e.g. the
-SSE connection cap in ``decnet.web.sse_limits``); the test does not
-forbid those — it only enforces the slowapi side.
-"""
-from decnet.web.api import app, _rate_limited_endpoint_names
-from fastapi.routing import APIRoute
-
-
-def _route_qualname_index() -> dict[tuple[str, str], str]:
-    idx: dict[tuple[str, str], str] = {}
-    for route in app.routes:
-        if not isinstance(route, APIRoute):
-            continue
-        qn = f"{route.endpoint.__module__}.{route.endpoint.__name__}"
-        for method in route.methods or ():
-            idx[(route.path, method.lower())] = qn
-    return idx
-
-
-def test_429_documented_on_rate_limited_endpoints_only() -> None:
-    schema = app.openapi()
-    paths = schema.get("paths", {})
-    assert paths, "OpenAPI schema is empty — router not mounted"
-
-    rate_limited = _rate_limited_endpoint_names()
-    assert rate_limited, "no @limiter.limit-decorated endpoints found"
-
-    qualname_for = _route_qualname_index()
-
-    http_methods = {"get", "post", "put", "patch", "delete", "options", "head"}
-    missing: list[str] = []
-
-    for path, item in paths.items():
-        for method, op in item.items():
-            if method.lower() not in http_methods:
-                continue
-            qn = qualname_for.get((path, method.lower()))
-            if qn in rate_limited and "429" not in op.get("responses", {}):
-                missing.append(f"{method.upper()} {path}")
-
-    assert not missing, f"rate-limited ops missing 429: {missing}"
-
-
-def test_login_endpoint_documents_429() -> None:
-    """Sanity check the one endpoint we know is rate-limited."""
-    schema = app.openapi()
-    op = schema["paths"]["/api/v1/auth/login"]["post"]
-    assert "429" in op["responses"]