Add is active to overridable entities and deactivation logic for page layouts (#19200)

- Replace soft-deletion (deletedAt) with isActive boolean for
overridable entities (tabs, widgets, viewFieldGroups, viewFields).
Standard entities are deactivated (isActive: false) when removed from
update payloads, while custom entities are hard-deleted.
- When a viewFieldGroup is deactivated/deleted, its viewFields are
reassigned to the next section by position (or null if none remain).
- Add isActive: true filters to viewFieldGroup and viewField API queries
so deactivated entities are excluded from responses.

Next: 
- fields-widget-upsert.service.ts should be refactored a bit
- Add restore logic

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

@@ -70,6 +70,7 @@ export const recomputeViewFieldIdentifierAfterFlatObjectIdentifierUpdate = ({
           updatedLabelIdentifierFieldMetadata.universalIdentifier,
         position: lowestViewFieldPosition - 1,
         isVisible: true,
+        isActive: true,
         size: DEFAULT_VIEW_FIELD_SIZE,
         viewId: flatView.id,
         viewUniversalIdentifier: flatView.universalIdentifier,