backfill widget position from gridPosition (phase 1 of gridPosition removal) (#20032)

## Context
Phase 1 of removing the legacy `gridPosition` field from
`PageLayoutWidget` in favor of the new `position` discriminated union
(`grid` / `vertical-list` / `canvas`). This PR is purely additive —
`gridPosition` is still required and read everywhere; we just guarantee
that every widget now also has a non-null `position` so a follow-up PR
can drop `gridPosition` cleanly.

## Changes
- **Slow instance command**
`BackfillPageLayoutWidgetPositionSlowInstanceCommand` (2.1.0):
for every `core.pageLayoutWidget` row where `position IS NULL`, copies
`gridPosition`
into `position` with `layoutMode: 'GRID'`. Historically only grid
widgets used
`gridPosition`, so a single SQL update covers every existing row.
- **`PageLayoutDuplicationService`**: when duplicating a widget, also
forwards
`originalWidget.position` (was previously only forwarding
`gridPosition`).
- **Frontend default layouts** (10 `Default*PageLayout.ts` files): added
a `position`
sibling to every widget, matching the parent tab's `layoutMode` —
`VERTICAL_LIST` widgets
get `{ layoutMode, index }`, `CANVAS` widgets get `{ layoutMode }`

<img width="338" height="226" alt="Screenshot 2026-04-24 at 16 23 17"
src="https://github.com/user-attachments/assets/c3319318-f1b8-4271-96b4-196b209a1f5e"
/>

packages/twenty-server/src/engine/metadata-modules/page-layout-widget/dtos/inputs/create-page-layout-widget.input.ts

@@ -39,7 +39,11 @@ export class CreatePageLayoutWidgetInput {
   @IsOptional()
   objectMetadataId?: string | null;
 
-  @Field(() => GridPositionInput, { nullable: false })
+  @Field(() => GridPositionInput, {
+    nullable: false,
+    deprecationReason:
+      'Use `position` instead. Will be removed in a future release.',
+  })
   @ValidateNested()
   @Type(() => GridPositionInput)
   gridPosition: GridPositionInput;

packages/twenty-server/src/engine/metadata-modules/page-layout-widget/dtos/inputs/update-page-layout-widget-with-id.input.ts

@@ -48,7 +48,10 @@ export class UpdatePageLayoutWidgetWithIdInput {
   @IsOptional()
   objectMetadataId: string | null;
 
-  @Field(() => GridPositionInput)
+  @Field(() => GridPositionInput, {
+    deprecationReason:
+      'Use `position` instead. Will be removed in a future release.',
+  })
   @ValidateNested()
   @Type(() => GridPositionInput)
   @IsNotEmpty()

packages/twenty-server/src/engine/metadata-modules/page-layout-widget/dtos/inputs/update-page-layout-widget.input.ts

@@ -42,7 +42,11 @@ export class UpdatePageLayoutWidgetInput {
   @IsOptional()
   objectMetadataId?: string | null;
 
-  @Field(() => GridPositionInput, { nullable: true })
+  @Field(() => GridPositionInput, {
+    nullable: true,
+    deprecationReason:
+      'Use `position` instead. Will be removed in a future release.',
+  })
   @ValidateNested()
   @Type(() => GridPositionInput)
   @IsOptional()

packages/twenty-server/src/engine/metadata-modules/page-layout-widget/dtos/page-layout-widget.dto.ts

@@ -56,7 +56,11 @@ export class PageLayoutWidgetDTO {
   @Field(() => UUIDScalarType, { nullable: true })
   objectMetadataId?: string;
 
-  @Field(() => GridPositionDTO, { nullable: false })
+  @Field(() => GridPositionDTO, {
+    nullable: false,
+    deprecationReason:
+      'Use `position` instead. Will be removed in a future release.',
+  })
   gridPosition: GridPositionDTO;
 
   @Field(() => PageLayoutWidgetPositionUnion, { nullable: true })

packages/twenty-server/src/engine/metadata-modules/page-layout/services/page-layout-duplication.service.ts

@@ -325,6 +325,7 @@ export class PageLayoutDuplicationService {
           createPageLayoutWidgetInput: {
             title: originalWidget.title,
             gridPosition: originalWidget.gridPosition,
+            position: originalWidget.position ?? undefined,
             type: originalWidget.type,
             objectMetadataId: originalWidget.objectMetadataId,
             configuration: originalWidget.configuration,