Pin every endpoint's behaviour with golden fixtures captured from the
retiring grpc-gateway (timestamps and secrets neutralised). Error cases
assert their HTTP status independently of the golden via assertStatus, so
a blind regenerate cannot re-pin a wrong code; HEADSCALE_UPDATE_GOLDEN
rewrites the fixtures. A unit test exercises the API-key auth middleware
on the real server router. Exclude the emitted spec and goldens from
pre-commit checks.
