feat(app-dev): add dry-run preview to dev sync (#21251)

Split out of #21240. Stacked on #21250 (review/merge that first).

`yarn twenty dev --once --dry-run` computes the migration plan and
prints the diff **without applying anything** (no migration, no
app-record update, no SDK generation). Also renders the diff on a normal
`dev --once` sync.

<img width="646" height="179" alt="image"
src="https://github.com/user-attachments/assets/59f3ddcd-2a5b-4b8a-b21a-c659abe16af0"
/>

packages/twenty-server/src/engine/workspace-manager/workspace-migration/services/workspace-migration-validate-build-and-run-service.ts

@@ -358,6 +358,7 @@ export class WorkspaceMigrationValidateBuildAndRunService {
   public async validateBuildAndRunWorkspaceMigrationFromTo(
     args: WorkspaceMigrationOrchestratorBuildArgs & {
       idByUniversalIdentifierByMetadataName?: IdByUniversalIdentifierByMetadataName;
+      dryRun?: boolean;
     },
   ): Promise<
     | WorkspaceMigrationOrchestratorFailedResult
@@ -365,7 +366,8 @@ export class WorkspaceMigrationValidateBuildAndRunService {
         hasSchemaMetadataChanged: boolean;
       })
   > {
-    const { idByUniversalIdentifierByMetadataName, ...buildArgs } = args;
+    const { idByUniversalIdentifierByMetadataName, dryRun, ...buildArgs } =
+      args;
 
     const validateAndBuildResult =
       await this.workspaceMigrationBuildOrchestratorService
@@ -392,7 +394,7 @@ export class WorkspaceMigrationValidateBuildAndRunService {
       workspaceMigration: validateAndBuildResult.workspaceMigration,
     });
 
-    if (workspaceMigration.actions.length === 0) {
+    if (dryRun === true || workspaceMigration.actions.length === 0) {
       return {
         status: 'success',
         workspaceMigration,