phsl / new-api

- Drop the unreachable user-visibility branch in LogOther.toMap and the
  receiver-mutating normalizeLegacyAdminFields; JSONString/Snapshot/
  MarshalJSON now share one full serialization
- Define legacySensitiveLogOtherKeys once and reference it from both
  SetPublic rejection and the user read-side projection
- Return the original JSON for every role when formatLogOtherJSON
  removed nothing, avoiding a re-marshal on the user log list path
- Log rejected OtherRatios keys in taskBillingOther instead of dropping
  them silently
- Use Snapshot() with typed assertions in service tests