fix: removeuseMergeRecordRelatationship and simplify dry run response (#15486)

## Description

- This PR addresses issue
https://github.com/twentyhq/twenty/issues/15201
- Removed
[useMergeRecordRelationships.ts](https://github.com/twentyhq/twenty/compare/main...harshit078:fix-merge-frontend?expand=1#diff-5d0366f814ff0c0e8961f40120690206a7acd3f7b66135cfb8c4ad8d3f6bc681)
- now backend returns populated result and frontend just shows it
without refetching relations.
- to be merged after PR- https://github.com/twentyhq/twenty/pull/15484


## Visual Appearance

 


https://github.com/user-attachments/assets/09d7548a-74a9-4742-af49-e98b4174f68c

---------

Co-authored-by: Etienne <45695613+etiennejouan@users.noreply.github.com>

packages/twenty-server/src/engine/api/common/common-query-runners/common-merge-many-query-runner.service.ts

@@ -134,9 +134,6 @@ export class CommonMergeManyQueryRunnerService extends CommonBaseQueryRunnerServ
     const recordsToMerge = await context.repository.find({
       where: { id: In(args.ids) },
       select: columnsToSelect,
-      ...(args.dryRun
-        ? { relations: args.selectedFieldsResult.relations }
-        : {}),
     });
 
     if (recordsToMerge.length !== args.ids.length) {
@@ -146,6 +143,23 @@ export class CommonMergeManyQueryRunnerService extends CommonBaseQueryRunnerServ
       );
     }
 
+    if (args.dryRun && args.selectedFieldsResult.relations) {
+      await this.processNestedRelationsHelper.processNestedRelations({
+        objectMetadataMaps: context.objectMetadataMaps,
+        parentObjectMetadataItem: context.objectMetadataItemWithFieldMaps,
+        parentObjectRecords: recordsToMerge as ObjectRecord[],
+        relations: args.selectedFieldsResult.relations as Record<
+          string,
+          FindOptionsRelations<ObjectLiteral>
+        >,
+        limit: QUERY_MAX_RECORDS,
+        authContext: context.authContext,
+        workspaceDataSource: context.workspaceDataSource,
+        rolePermissionConfig: context.rolePermissionConfig,
+        selectedFields: args.selectedFieldsResult.select,
+      });
+    }
+
     return recordsToMerge as ObjectRecord[];
   }