feat: release configurable API response contracts

Define reusable response bodies in .api with typed code mappings, per-route overrides and matching OpenAPI schemas. Add application and callback encoders, early response policy selection, and isolated remote-consumer release verification.

Release v0.8.0-preview after full race, vet, build and local MySQL workflow acceptance.

config/file.go

@@ -181,6 +181,7 @@ func (r *Reloader) Snapshot() Config {
 	r.mu.Lock()
 	defer r.mu.Unlock()
 	cfg := r.current
+	cfg.Response = r.current.Response.Clone()
 	cfg.TrustedProxies = append([]string(nil), cfg.TrustedProxies...)
 	cfg.Log.RedactKeys = append([]string(nil), cfg.Log.RedactKeys...)
 	return cfg