feat: allow apps to add view fields to existing views (defineViewField) (#21160)

## Summary

Lets a Twenty application add **view fields (columns) to an existing
view it does not own** — including standard views like the People index
view — without redeclaring/owning that view. This mirrors the existing,
working pattern by which an app adds a custom field to a standard object
via `defineField` + `objectUniversalIdentifier`.

The asymmetry being removed was purely in the manifest schema:
`ViewFieldManifest` only existed *nested* inside
`ViewManifest.fields[]`, so adding a view field forced declaring a
`ViewManifest` — which the sync treats as a view the app creates and
owns, and rejects when the UID is a standard view's. Validation,
persistence, the FK aggregator machinery, and uninstall cleanup were
already generic and cross-app-safe, so no engine changes were needed.

### Changes
- **twenty-shared:** new top-level `StandaloneViewFieldManifest`
(`ViewFieldManifest & { viewUniversalIdentifier }`),
`Manifest.viewFields`, and a `SyncableEntity.ViewField` member.
- **twenty-sdk:** `defineViewField` (validates `universalIdentifier` +
`viewUniversalIdentifier` + `fieldMetadataUniversalIdentifier`), CLI
manifest assembly of a top-level `viewFields` list, and `dev:add
viewField` scaffolding.
- **twenty-server:** one top-level loop over `manifest.viewFields` that
reuses the existing `fromViewFieldManifestToUniversalFlatViewField`
converter (already parameterized by `viewUniversalIdentifier`). No
validator/persistence/aggregator changes.

### Notes for maintainers
- Confirm the `Manifest.viewFields` optionality convention — implemented
as a **required** array to mirror `fields`/`views`.
- Two different apps adding a column for the same field to the same view
conflicts on the existing unique `(fieldMetadataId, viewId)` partial
index; the existing `flat-view-field-validator` duplicate check surfaces
this as a structured validation error.
- `dev:add viewField` scaffolding is included (was optional in the
plan).

## Test Plan
- [x] `twenty-shared` typecheck
- [x] `twenty-sdk` 364 unit tests + `buildManifest` assembly test
(rich-app fixture) + typecheck + prettier
- [x] `twenty-server` typecheck + `lint:diff-with-main`
- [x] **Server integration suite**
`successful-manifest-update-view-field.integration-spec.ts` (4/4):
- standalone view field attaches to the standard `allPeople` view
without recreating it (sync succeeds, no
`INVALID_VIEW_DATA`/`ENTITY_ALREADY_EXISTS`)
- uninstall removes the contributed column while the standard view + its
columns remain intact
  - duplicate `(view, field)` rejected with `METADATA_VALIDATION_FAILED`
  - unknown target view rejected
- [x] Sibling `successful-manifest-update-field.integration-spec.ts`
still green (no harness regression)

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

packages/twenty-shared/src/application/enums/syncable-entities.enum.ts

@@ -8,6 +8,7 @@ export enum SyncableEntity {
   Agent = 'agent',
   ConnectionProvider = 'connectionProvider',
   View = 'view',
+  ViewField = 'viewField',
   NavigationMenuItem = 'navigationMenuItem',
   PageLayout = 'pageLayout',
   PageLayoutTab = 'pageLayoutTab',

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

@@ -75,6 +75,7 @@ export type { ToolTriggerSettings } from './toolTriggerSettingsType';
 export type {
   ViewManifestFilterValue,
   ViewFieldManifest,
+  StandaloneViewFieldManifest,
   ViewFilterManifest,
   ViewFilterGroupManifest,
   ViewGroupManifest,

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

@@ -18,7 +18,10 @@ import {
 import { type PermissionFlagManifest } from './permissionFlagManifestType';
 import { type RoleManifest } from './roleManifestType';
 import { type SkillManifest } from './skillManifestType';
-import { type ViewManifest } from './viewManifestType';
+import {
+  type StandaloneViewFieldManifest,
+  type ViewManifest,
+} from './viewManifestType';
 
 export type Manifest = {
   application: ApplicationManifest;
@@ -34,6 +37,7 @@ export type Manifest = {
   connectionProviders?: ConnectionProviderManifest[];
   publicAssets: AssetManifest[];
   views: ViewManifest[];
+  viewFields: StandaloneViewFieldManifest[];
   navigationMenuItems: NavigationMenuItemManifest[];
   pageLayouts: PageLayoutManifest[];
   pageLayoutTabs: PageLayoutTabManifest[];

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

@@ -1,10 +1,10 @@
 import { type SyncableEntityOptions } from '@/application/syncableEntityOptionsType';
 import {
-  type ViewKey,
   type AggregateOperations,
   type ViewCalendarLayout,
   type ViewFilterGroupLogicalOperator,
   type ViewFilterOperand,
+  type ViewKey,
   type ViewOpenRecordIn,
   type ViewSortDirection,
   type ViewType,
@@ -27,6 +27,10 @@ export type ViewFieldManifest = SyncableEntityOptions & {
   viewFieldGroupUniversalIdentifier?: string;
 };
 
+export type StandaloneViewFieldManifest = ViewFieldManifest & {
+  viewUniversalIdentifier: string;
+};
+
 export type ViewFilterManifest = SyncableEntityOptions & {
   fieldMetadataUniversalIdentifier: string;
   operand: ViewFilterOperand;