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/object-metadata/dtos/object-metadata.dto.ts

@@ -77,8 +77,8 @@ export class ObjectMetadataDTO {
   @HideField()
   workspaceId: string;
 
-  @Field(() => UUIDScalarType, { nullable: true })
-  applicationId?: string;
+  @Field(() => UUIDScalarType)
+  applicationId: string;
 
   @Field()
   createdAt: Date;