feat: add project-owned error catalogs and HTTP 200 failure contracts

config/env.go

@@ -19,6 +19,7 @@ func LoadFromEnv(prefix string) (Config, error) {
 // ApplyEnv overlays nonempty environment values on a caller's defaults or file
 // settings, then validates the result. Caller-owned slices are not retained.
 func ApplyEnv(defaults Config, prefix string) (Config, error) {
+	defaults.Errors = defaults.Errors.Clone()
 	defaults.TrustedProxies = append([]string(nil), defaults.TrustedProxies...)
 	defaults.Log.RedactKeys = append([]string(nil), defaults.Log.RedactKeys...)
 	return applyEnv(defaults, prefix)