fix: restore isCustom gate in metadata label resolvers (#21432)

## Context

#21228 removed the stored `isCustom` column and, with it, the `isCustom`
early-return in `resolveObjectMetadataStandardOverride` /
`resolveFieldMetadataStandardOverride`, on the assumption that falling
through the `standardOverrides` checks was equivalent.

It isn't: custom object/field labels now reach the Lingui lookup. A
custom label that collides with a standard catalog string (e.g. a custom
field labeled "Status") gets translated for non-English locales against
the user's intent, and every other custom label pays a hash + catalog
miss — and, in production, an "Uncompiled message detected" warning
(#21415) — on each metadata resolution.

## Fix

Restore the gate. `isCustom` is no longer stored, so call sites that
build the resolver input from flat entities (dataloader,
minimal-metadata, view controller, command-menu-item navigation context)
derive it via `belongsToTwentyStandardApp`; GraphQL resolvers keep
passing DTOs, which already carry the derived value.

## Testing

- Unit tests for both resolvers, including a new regression test: a
custom label matching a standard catalog entry is returned verbatim,
Lingui never called.

---------

Co-authored-by: Weiko <corentin@twenty.com>

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

@@ -22,6 +22,7 @@ import { findFlatEntityByIdInFlatEntityMapsOrThrow } from 'src/engine/metadata-m
 import { findManyFlatEntityByIdInFlatEntityMaps } from 'src/engine/metadata-modules/flat-entity/utils/find-many-flat-entity-by-id-in-flat-entity-maps.util';
 import { findManyFlatEntityByIdInFlatEntityMapsOrThrow } from 'src/engine/metadata-modules/flat-entity/utils/find-many-flat-entity-by-id-in-flat-entity-maps-or-throw.util';
 import { fromFlatFieldMetadataToFieldMetadataDto } from 'src/engine/metadata-modules/flat-field-metadata/utils/from-flat-field-metadata-to-field-metadata-dto.util';
+import { belongsToTwentyStandardApp } from 'src/engine/metadata-modules/utils/belongs-to-twenty-standard-app.util';
 import { isFlatFieldMetadataOfType } from 'src/engine/metadata-modules/flat-field-metadata/utils/is-flat-field-metadata-of-type.util';
 import { resolveMorphRelationsFromFlatFieldMetadata } from 'src/engine/metadata-modules/flat-field-metadata/utils/resolve-morph-relations-from-flat-field-metadata.util';
 import { resolveRelationFromFlatFieldMetadata } from 'src/engine/metadata-modules/flat-field-metadata/utils/resolve-relation-from-flat-field-metadata.util';
@@ -336,6 +337,8 @@ export class DataloaderService {
                         label: flatFieldMetadata.label,
                         description: flatFieldMetadata.description ?? undefined,
                         icon: flatFieldMetadata.icon ?? undefined,
+                        isCustom:
+                          !belongsToTwentyStandardApp(flatFieldMetadata),
                         standardOverrides:
                           flatFieldMetadata.standardOverrides ?? undefined,
                       },