fix(server): enforce lowercase universalIdentifier in sync (#21754)

## Context

App sync fails when a manifest defines an entity with an uppercase UUID
`universalIdentifier`. Postgres `uuid` columns normalize to lowercase on
write, but the sync diff matches `universalIdentifier` strings
case-sensitively. So an uppercase-defined entity never matches its
lowercased DB row and is seen as delete + create on every sync, which
trips downstream guards like "Parent navigation menu item not found".

## Change

Reject non-lowercase `universalIdentifier`s at validation time in
`WorkspaceEntityMigrationBuilderService.validateUniversalIdentifier`
(right after the existing UUID-v4 check). This lives in the abstract
base builder, so it covers every syncable entity type. App authors now
get a clear "must be lowercase" error on the first sync instead of
confusing downstream failures.

Validation is sufficient here, no normalization needed — because the DB
side is always lowercase, so rejecting uppercase input guarantees both
sides of the diff match.

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packages/twenty-server/src/engine/workspace-manager/workspace-migration/workspace-migration-builder/services/workspace-entity-migration-builder.service.ts

@@ -390,6 +390,16 @@ export abstract class WorkspaceEntityMigrationBuilderService<
       ];
     }
 
+    if (universalIdentifier !== universalIdentifier.toLowerCase()) {
+      return [
+        {
+          code: FlatEntityMapsExceptionCode.ENTITY_MALFORMED,
+          message: `Invalid universalIdentifier: "${universalIdentifier}" must be lowercase`,
+          value: universalIdentifier,
+        },
+      ];
+    }
+
     return [];
   }