feat(twenty-server): allow shouldHideEmptyGroups in app view manifest (#21370)

## Context

The view **Hide empty groups** setting (`shouldHideEmptyGroups`) can be
toggled in the UI, is persisted on the `View` entity, exposed in the
`CreateView`/`UpdateView` GraphQL inputs, and tracked by the flat-view
sync machinery — but it could **not** be set from an app's view
manifest.

Root cause: the field postdates the manifest plumbing (added in #16385,
Dec 2025). Two spots were never updated to thread it through:
- `ViewManifest` didn't declare the field.
- `fromViewManifestToUniversalFlatView` hardcoded
`shouldHideEmptyGroups: false`.

Ref: twentyhq/core-team-issues#414

## Changes

- Add optional `shouldHideEmptyGroups?: boolean` to `ViewManifest`.
- Read it in the converter (`?? false`), mirroring the existing
`isCompact` handling.
- Cover it in the converter unit test (default + explicit value).

No migration or schema change — the column already exists, and
downstream sync (`FLAT_VIEW_EDITABLE_PROPERTIES` + the universal-flat
compare type) already handles it.

## Test

- `npx jest from-view-manifest-to-universal-flat-view` → 5 passed
- `tsgo -p tsconfig.json` (twenty-server) → no new errors
- oxlint + oxfmt clean

packages/twenty-shared/src/application/viewManifestType.ts

@@ -74,6 +74,7 @@ export type ViewManifest = SyncableEntityOptions & {
   visibility?: ViewVisibility;
   openRecordIn?: ViewOpenRecordIn;
   mainGroupByFieldMetadataUniversalIdentifier?: string;
+  shouldHideEmptyGroups?: boolean;
   kanbanAggregateOperation?: AggregateOperations;
   kanbanAggregateOperationFieldMetadataUniversalIdentifier?: string;
   calendarLayout?: ViewCalendarLayout;