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-front/src/generated-metadata/graphql.ts

@@ -3315,6 +3315,7 @@ export type MutationStopAgentChatStreamArgs = {
 
 
 export type MutationSyncApplicationArgs = {
+  dryRun?: InputMaybe<Scalars['Boolean']>;
   manifest: Scalars['JSON'];
 };