feat(sdk): add defineCommandMenuItem (#20256)

## Summary

- Add `defineCommandMenuItem` and `definePageLayoutWidget` as standalone
SDK defines, mirroring the existing `definePageLayoutTab` pattern. Both
entities can still be declared nested inside their parent
(`defineFrontComponent.command` / `definePageLayout.tabs[].widgets[]`).
- Add `CommandMenuItem` and `PageLayoutWidget` to the `SyncableEntity`
enum and the dev-mode UI labels.
- Wire the SDK manifest-build to extract the two new defines into
top-level `commandMenuItems` / `pageLayoutWidgets` arrays on the
manifest, and the server aggregator to consume them through the existing
flat-entity converters.
- On the server, expose `Application.commandMenuItems` (relation + DTO +
service hydration in `findOneApplication`).
- On the front, list command menu items in the application content tab
and add a dedicated detail page with a settings tab, mirroring how
`frontComponents` are surfaced.
- Add `twenty add` templates and Vitest unit tests for both new defines.
- Document the standalone-vs-nested pattern in
`packages/twenty-sdk/README.md`.

### Why

Until now, command menu items could only be declared as the nested
`command:` field on `defineFrontComponent` — there was no way to
register a command menu item from a separate file or from another
package. The `SyncableEntity` enum had 12 values, while the server
already synced 18 (including `commandMenuItem` and `pageLayoutWidget`).
The same gap existed for `pageLayoutWidget`, which had no top-level
define despite being synced server-side. This PR closes both gaps and
aligns the SDK surface with what the server actually accepts.

The standalone defines coexist with the nested form — pick one per
entity, never both with the same `universalIdentifier` (the manifest
aggregator will throw on duplicates). The README now documents this.

## Test plan

- [x] `npx nx typecheck twenty-sdk` / `twenty-server` / `twenty-front`
- [x] `npx nx lint:diff-with-main twenty-front` / `twenty-server`
- [x] `npx nx lint twenty-sdk` / `twenty-shared`
- [x] New unit tests: `define-command-menu-item.spec.ts`,
`define-page-layout-widget.spec.ts`
- [x] Existing manifest extract config tests still pass
- [ ] Codegen `npx nx run twenty-front:graphql:generate
--configuration=metadata` should be re-run after merge — the generated
`graphql.ts` was patched manually to include `commandMenuItems` on
`Application` and the `FindOneApplication` document.
- [ ] Smoke test: scaffold an app with `twenty add` for both new entity
types, run `twenty dev`, confirm the dev UI shows them in the sync list
and the settings page surfaces command menu items in the content tab.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: martmull <martmull@hotmail.fr>
Co-authored-by: Charles Bochet <charles@twenty.com>

packages/twenty-server/src/engine/metadata-modules/command-menu-item/dtos/command-menu-item.dto.ts

@@ -99,6 +99,9 @@ export class CommandMenuItemDTO {
   @HideField()
   workspaceId: string;
 
+  @Field(() => UUIDScalarType, { nullable: true })
+  universalIdentifier?: string;
+
   @Field(() => UUIDScalarType, { nullable: true })
   applicationId?: string;