fix: use pickMorphGroupSurvivor in relation loader to match field metadata deduplication (#17988)

## Summary

- Fixes "Target field metadata full object not found" error thrown
during optimistic effects (e.g., bulk delete) on workspaces with custom
objects
- The relation loader was using a simple sort-by-ID to pick the
representative morph field, while `filterMorphRelationDuplicateFields`
uses `pickMorphGroupSurvivor` which prefers active non-system fields.
When a custom object's auto-created morph field (`isSystem: true`)
happened to have the smallest UUID, the two loaders would disagree — the
relation DTO pointed to that system field's ID, but the field metadata
loader filtered it out in favor of a standard field, causing the
frontend lookup to fail.
- Now both code paths use `pickMorphGroupSurvivor` so they always agree
on which morph field represents the group.

## Test plan

- [ ] Create a custom object on a workspace that already has standard
objects with morph relations (e.g., noteTarget, taskTarget)
- [ ] Bulk-select and delete records (e.g., People) — should no longer
throw "Target field metadata full object not found"

Made with [Cursor](https://cursor.com)

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Small, localized change to morph-relation selection logic in a
dataloader; main risk is altered field choice for edge-case morph
groups, but behavior now matches existing deduplication.
> 
> **Overview**
> Ensures the relation dataloader picks the representative
morph-relation target field using `pickMorphGroupSurvivor` (preferring
active non-system fields) instead of the previous sort-by-id approach.
> 
> This aligns `createRelationLoader` with
`filterMorphRelationDuplicateFields`, preventing mismatches where
relation DTOs could reference a morph field that gets filtered out
elsewhere (e.g., triggering “Target field metadata full object not
found”).
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
c3a6d861262cd21c49cb7582767d419e8048980d. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Co-authored-by: Cursor <cursoragent@cursor.com>

packages/twenty-server/src/engine/dataloaders/dataloader.service.ts

@@ -10,6 +10,7 @@ import { type IndexMetadataInterface } from 'src/engine/metadata-modules/index-m
 import { I18nService } from 'src/engine/core-modules/i18n/i18n.service';
 import { type IDataloaders } from 'src/engine/dataloaders/dataloader.interface';
 import { filterMorphRelationDuplicateFields } from 'src/engine/dataloaders/utils/filter-morph-relation-duplicate-fields.util';
+import { pickMorphGroupSurvivor } from 'src/engine/dataloaders/utils/pick-morph-group-survivor.util';
 import { FIELD_METADATA_STANDARD_OVERRIDES_PROPERTIES } from 'src/engine/metadata-modules/field-metadata/constants/field-metadata-standard-overrides-properties.constant';
 import { type FieldMetadataDTO } from 'src/engine/metadata-modules/field-metadata/dtos/field-metadata.dto';
 import { RelationDTO } from 'src/engine/metadata-modules/field-metadata/dtos/relation.dto';
@@ -188,14 +189,18 @@ export class DataloaderService {
                 flatFieldMetadataMaps,
                 flatObjectMetadata: targetFlatObjectMetadata,
               }),
-            ].sort((a, b) => (a.id > b.id ? 1 : -1));
+            ];
+
+            const survivorMorphField = pickMorphGroupSurvivor(
+              allMorphFlatFieldMetadatas,
+            );
 
             relationDtos.push(
               fromMorphOrRelationFlatFieldMetadataToRelationDto({
                 sourceFlatFieldMetadata,
                 sourceFlatObjectMetadata,
                 targetFlatFieldMetadata: {
-                  ...allMorphFlatFieldMetadatas[0],
+                  ...survivorMorphField,
                   name: morphNameFromMorphFieldMetadataName,
                 },
                 targetFlatObjectMetadata,