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-sdk/src/cli/commands/dev/dev-once.ts

@@ -7,6 +7,7 @@ import chalk from 'chalk';
 export type AppDevOnceCommandOptions = {
   appPath?: string;
   verbose?: boolean;
+  dryRun?: boolean;
 };
 
 export class AppDevOnceCommand {
@@ -17,12 +18,17 @@ export class AppDevOnceCommand {
 
     const remoteName = ConfigService.getActiveRemote();
 
-    console.log(chalk.blue(`Syncing application on ${remoteName}...`));
+    console.log(
+      chalk.blue(
+        `${options.dryRun ? 'Previewing application diff' : 'Syncing application'} on ${remoteName}...`,
+      ),
+    );
     console.log(chalk.gray(`App path: ${appPath}\n`));
 
     const result = await appDevOnce({
       appPath,
       verbose: options.verbose,
+      dryRun: options.dryRun,
       onProgress: (message) => console.log(chalk.gray(message)),
     });
 
@@ -31,6 +37,16 @@ export class AppDevOnceCommand {
       process.exit(1);
     }
 
+    if (options.dryRun) {
+      console.log(
+        chalk.green(
+          `\n✓ Dry run complete for ${result.data.applicationDisplayName} — no changes were applied`,
+        ),
+      );
+
+      return;
+    }
+
     console.log(
       chalk.green(
         `\n✓ Synced ${result.data.applicationDisplayName} (${result.data.fileCount} file${result.data.fileCount === 1 ? '' : 's'})`,

packages/twenty-sdk/src/cli/commands/dev/index.ts

@@ -22,6 +22,7 @@ export const registerDevCommands = (program: Command): void => {
       verbose?: boolean;
       debug?: boolean;
       debounceMs?: string;
+      dryRun?: boolean;
     },
   ) => {
     const commonOptions = {
@@ -33,7 +34,10 @@ export const registerDevCommands = (program: Command): void => {
     };
 
     if (options.once) {
-      await devOnceCommand.execute(commonOptions);
+      await devOnceCommand.execute({
+        ...commonOptions,
+        dryRun: options.dryRun,
+      });
 
       return;
     }
@@ -48,6 +52,10 @@ export const registerDevCommands = (program: Command): void => {
       '-o, --once',
       'Build and sync once, then exit (useful for CI, scripts, and pre-commit hooks)',
     )
+    .option(
+      '--dry-run',
+      'Preview the metadata changes without applying them (requires --once)',
+    )
     .option('--debounceMs <ms>', 'Debounce in ms (default: 2 000)')
     .option('-v, --verbose', 'Show detailed logs')
     .option('-d, --debug', 'Show detailed logs (alias for --verbose)')