Previous commit advertised 429 on every operation. Only routes
decorated with @limiter.limit can actually return slowapi's 429 —
currently just POST /api/v1/auth/login. Documenting it elsewhere is
dishonest and would mislead clients into expecting a response the
server cannot produce.
Walk slowapi's _route_limits / _dynamic_route_limits registries to
identify decorated endpoints, match them to FastAPI routes by
{module}.{name}, and only inject 429 on those.
Existing per-route 429 declarations (e.g. SSE connection-cap on
events streams via sse_limits) are untouched.
SlowAPI middleware can short-circuit any request with 429 once a
per-route or per-IP rate limit fires (e.g. POST /api/v1/auth/login is
capped at 10/5min). The OpenAPI spec did not declare 429 on any
operation, so schemathesis flagged legitimate rate-limit responses as
RejectedPositiveData / status-code-nonconformance failures.
Override app.openapi to inject a generic 429 response object on every
HTTP operation in the generated schema. Add a contract test that fails
if any operation drops the 429 advertisement.
