refactor: stop reading joinColumnName from relation field settings (#20304)

## Summary

`joinColumnName` on relation field settings is always derivable from the
field name (and the target object name for morph relations). This PR
stops reading it from settings anywhere in production code; the stored
value is no longer used.

The settings field is **not** removed from data yet — a follow-up can
drop it once we are confident nothing depends on the stored value.

## Helpers

The helpers are split by layer because frontend and backend hold morph
relations differently: the frontend has a base name plus a
`morphRelations[]` array, the backend has one row per target with the
name already morph-resolved.

| Helper | Layer | When to use |
|---|---|---|
| `computeRelationGqlFieldJoinColumnName` | Shared / frontend
(`gqlField`) | Non-morph relation on the frontend. |
| `computeMorphRelationGqlFieldName` | Shared / frontend (`gqlField`) |
Need the per-target morph gqlField name (e.g. `targetCompany`). |
| `computeMorphRelationGqlFieldJoinColumnName` | Shared / frontend
(`gqlField`) | Per-target morph join column on the frontend. Prefer over
the non-morph helper for any morph field — it forces the per-target
inputs. |
| `computeMorphOrRelationFieldJoinColumnName` | Backend
(`FlatFieldMetadata.name`) | Any backend read or write — the flat name
is already morph-resolved, so one helper covers both cases. |
| `computeMorphRelationFlatFieldName` | Backend
(`FlatFieldMetadata.name`) | **Mutation paths only** (create / update /
object rename). Reads consume the stored `field.name` and never call
this. |

## Test plan

- [x] Typecheck and lint (front, server, shared)
- [x] Existing unit tests pass
- [ ] CI green

packages/twenty-server/src/engine/api/common/common-args-processors/data-arg-processor/data-arg-processor.service.ts

@@ -14,6 +14,7 @@ import {
   isDefined,
 } from 'twenty-shared/utils';
 
+import { computeMorphOrRelationFieldJoinColumnName } from 'src/engine/metadata-modules/field-metadata/utils/compute-morph-or-relation-field-join-column-name.util';
 import { transformActorField } from 'src/engine/api/common/common-args-processors/data-arg-processor/transformer-utils/transform-actor-field.util';
 import { transformAddressField } from 'src/engine/api/common/common-args-processors/data-arg-processor/transformer-utils/transform-address-field.util';
 import { transformArrayField } from 'src/engine/api/common/common-args-processors/data-arg-processor/transformer-utils/transform-array-field.util';
@@ -56,12 +57,10 @@ import { transformLinksValue } from 'src/engine/core-modules/record-transformer/
 import { transformPhonesValue } from 'src/engine/core-modules/record-transformer/utils/transform-phones-value.util';
 import { transformRichTextValue } from 'src/engine/core-modules/record-transformer/utils/transform-rich-text.util';
 import { WorkspaceNotFoundDefaultError } from 'src/engine/core-modules/workspace/workspace.exception';
-import { computeMorphOrRelationFieldJoinColumnName } from 'src/engine/metadata-modules/field-metadata/utils/compute-morph-or-relation-field-join-column-name.util';
 import { FlatEntityMaps } from 'src/engine/metadata-modules/flat-entity/types/flat-entity-maps.type';
 import { findFlatEntityByIdInFlatEntityMaps } from 'src/engine/metadata-modules/flat-entity/utils/find-flat-entity-by-id-in-flat-entity-maps.util';
 import { FlatFieldMetadata } from 'src/engine/metadata-modules/flat-field-metadata/types/flat-field-metadata.type';
 import { buildFieldMapsFromFlatObjectMetadata } from 'src/engine/metadata-modules/flat-field-metadata/utils/build-field-maps-from-flat-object-metadata.util';
-import { isFlatFieldMetadataOfType } from 'src/engine/metadata-modules/flat-field-metadata/utils/is-flat-field-metadata-of-type.util';
 import { FlatObjectMetadata } from 'src/engine/metadata-modules/flat-object-metadata/types/flat-object-metadata.type';
 
 @Injectable()
@@ -245,14 +244,9 @@ export class DataArgProcessorService {
           );
         }
 
-        const joinColumnName = isFlatFieldMetadataOfType(
-          fieldMetadata,
-          FieldMetadataType.MORPH_RELATION,
-        )
-          ? computeMorphOrRelationFieldJoinColumnName({
-              name: fieldMetadata.name,
-            })
-          : relationSettings.joinColumnName;
+        const joinColumnName = computeMorphOrRelationFieldJoinColumnName({
+          name: fieldMetadata.name,
+        });
 
         if (key === joinColumnName) {
           return validateUUIDFieldOrThrow(value, key);

packages/twenty-server/src/engine/api/common/common-args-processors/filter-arg-processor/filter-arg-processor.service.ts

@@ -8,6 +8,7 @@ import {
 } from 'twenty-shared/types';
 import { isDefined } from 'twenty-shared/utils';
 
+import { computeMorphOrRelationFieldJoinColumnName } from 'src/engine/metadata-modules/field-metadata/utils/compute-morph-or-relation-field-join-column-name.util';
 import { type ObjectRecordFilter } from 'src/engine/api/graphql/workspace-query-builder/interfaces/object-record.interface';
 
 import { validateAndTransformOperatorAndValue } from 'src/engine/api/common/common-args-processors/filter-arg-processor/utils/validate-and-transform-operator-and-value.util';
@@ -17,7 +18,6 @@ import {
 } from 'src/engine/api/common/common-query-runners/errors/common-query-runner.exception';
 import { STANDARD_ERROR_MESSAGE } from 'src/engine/api/common/common-query-runners/errors/standard-error-message.constant';
 import { type CompositeFieldMetadataType } from 'src/engine/metadata-modules/field-metadata/types/composite-field-metadata-type.type';
-import { computeMorphOrRelationFieldJoinColumnName } from 'src/engine/metadata-modules/field-metadata/utils/compute-morph-or-relation-field-join-column-name.util';
 import { isCompositeFieldMetadataType } from 'src/engine/metadata-modules/field-metadata/utils/is-composite-field-metadata-type.util';
 import { FlatEntityMaps } from 'src/engine/metadata-modules/flat-entity/types/flat-entity-maps.type';
 import { findFlatEntityByIdInFlatEntityMaps } from 'src/engine/metadata-modules/flat-entity/utils/find-flat-entity-by-id-in-flat-entity-maps.util';