[FRONT COMPONENTS] Headless components (#18096)

## Description

- Add `isHeadless` field to `FrontComponent` entity so front components
can run without rendering UI in the command menu
- Introduce headless front component mounting logic:
`HeadlessFrontComponentMountRoot` at the application root,
`useMountHeadlessFrontComponent`, and `useUnmountHeadlessFrontComponent`
hooks to mount/unmount headless components
- Expand the SDK with new action components (`Action`, `ActionLink`,
`ActionOpenSidePanelPage`) and host communication functions
(`openSidePanelPage`, `unmountFrontComponent`)
- Move `CommandMenuPages` type to twenty-shared so the SDK can reference
it for side panel navigation

## Video QA



https://github.com/user-attachments/assets/4f9e3bb1-fcd1-42be-b3f4-a97e80c2add2

packages/twenty-server/src/engine/metadata-modules/front-component/dtos/front-component.dto.ts

@@ -1,6 +1,7 @@
 import { Field, HideField, ObjectType } from '@nestjs/graphql';
 
 import {
+  IsBoolean,
   IsDateString,
   IsNotEmpty,
   IsOptional,
@@ -63,6 +64,10 @@ export class FrontComponentDTO {
   @Field()
   updatedAt: Date;
 
+  @IsBoolean()
+  @Field()
+  isHeadless: boolean;
+
   @Field(() => ApplicationTokenPairDTO, { nullable: true })
   applicationTokenPair?: ApplicationTokenPairDTO;
 }

packages/twenty-server/src/engine/metadata-modules/front-component/entities/front-component.entity.ts

@@ -34,6 +34,9 @@ export class FrontComponentEntity
   @Column({ nullable: false })
   builtComponentChecksum: string;
 
+  @Column({ default: false })
+  isHeadless: boolean;
+
   @CreateDateColumn({ type: 'timestamptz' })
   createdAt: Date;