Identification cleanup (#17301)

# Introduction

following https://github.com/twentyhq/twenty/pull/17279
As we've finally identified all the syncable metadata entities, which
means they're expected to have non nullable applicationId and
universalIdentifier at pg_level we can remove previous retro comp
universalIdentifier fallbacking and update the dto too

~~This needs IdentifyRemainingEntitiesMetadataCommand and
MakeRemainingEntitiesUniversalIdentifierAndApplicationIdNotNullableMigrationCommand
to be run~~
```ts
[Nest] 197  - 01/21/2026, 3:08:35 PM     LOG [MakeRemainingEntitiesUniversalIdentifierAndApplicationIdNotNullableMigrationCommand] Successfully run MakeRemainingEntitiesUniversalIdentifierAndApplicationIdNotNullableMigrationCommand
```

packages/twenty-server/src/engine/metadata-modules/flat-index-metadata/utils/from-index-metadata-entity-to-flat-index-metadata.util.ts

@@ -17,8 +17,7 @@ export const fromIndexMetadataEntityToFlatIndexMetadata = (
     createdAt: indexMetadataEntity.createdAt.toISOString(),
     updatedAt: indexMetadataEntity.updatedAt.toISOString(),
     universalIdentifier:
-      indexMetadataEntityWithoutRelations.universalIdentifier ??
-      indexMetadataEntityWithoutRelations.id,
+      indexMetadataEntityWithoutRelations.universalIdentifier,
     flatIndexFieldMetadatas: indexMetadataEntity.indexFieldMetadatas.map(
       (indexFieldMetadata) => ({
         ...removePropertiesFromRecord(indexFieldMetadata, [