[Apps] Fix - app-synced object should be searchable (#19206)

## Summary

- **Make app-synced objects searchable**: `isSearchable` was hardcoded
to `false` and the `searchVector` field was missing the `GENERATED
ALWAYS AS (...)` expression, causing all records to have a `NULL` search
vector and be excluded from search results. Fixed by defaulting
`isSearchable` to `true` (configurable via the object manifest),
computing the `asExpression` from the label identifier field, and
allowing the update-field-action-handler to handle the `null` → defined
`asExpression` transition.
- **Make `isSearchable` updatable on an object**: The property had
`toCompare: false` in the entity properties configuration, so updates
via the API were silently ignored and never persisted. Fixed by setting
`toCompare: true`.

packages/twenty-server/src/engine/metadata-modules/flat-object-metadata/utils/recompute-search-vector-field-after-label-identifier-update.util.ts

@@ -1,5 +1,9 @@
 import { type FieldMetadataType } from 'twenty-shared/types';
-import { findOrThrow, isDefined } from 'twenty-shared/utils';
+import {
+  findOrThrow,
+  isDefined,
+  type SearchableFieldType,
+} from 'twenty-shared/utils';
 
 import { type AllFlatEntityMaps } from 'src/engine/metadata-modules/flat-entity/types/all-flat-entity-maps.type';
 import { findFlatEntityByUniversalIdentifier } from 'src/engine/metadata-modules/flat-entity/utils/find-flat-entity-by-universal-identifier.util';
@@ -12,7 +16,6 @@ import {
 } from 'src/engine/metadata-modules/object-metadata/object-metadata.exception';
 import { SEARCH_VECTOR_FIELD } from 'src/engine/metadata-modules/search-field-metadata/constants/search-vector-field.constants';
 import { getTsVectorColumnExpressionFromFields } from 'src/engine/workspace-manager/utils/get-ts-vector-column-expression.util';
-import { type SearchableFieldType } from 'src/engine/workspace-manager/utils/is-searchable-field.util';
 
 type RecomputeSearchVectorFieldAfterLabelIdentifierUpdateArgs = {
   existingFlatObjectMetadata: FlatObjectMetadata;