feat(app-dev): sync error hints, flatEntity labels, dev-mode summary UI, and docs (#21252)

Split out of #21240 — all remaining app-dev improvements. Stacked on
#21251 (review/merge that first).

- Actionable recovery hints on failed syncs; unified diff renderer;
`--dry-run` guard.
- Return `flatEntity` on update/delete sync actions and unify the diff
label.
- Summarize the dev-mode entity list unless `--verbose`.
- Docs: syncing & recovery guide + dry-run + open-an-issue prompt.
- Live execution mode for synced logic functions; clearer manifest
warnings.

<img width="1018" height="700" alt="image"
src="https://github.com/user-attachments/assets/5e9ce19e-0f1d-4f99-8524-4e118bde932b"
/>

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

@@ -45,7 +45,7 @@ export class AppDevCommand {
 
       orchestratorState.onChange = () => uiStateManager.notify();
 
-      const { unmount } = await renderDevUI(uiStateManager);
+      const { unmount } = await renderDevUI(uiStateManager, options.verbose);
 
       this.unmountUI = unmount;
 

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

@@ -1,4 +1,5 @@
 import { formatPath } from '@/cli/utilities/file/file-path';
+import chalk from 'chalk';
 import type { Command } from 'commander';
 import { SyncableEntity } from 'twenty-shared/application';
 import { EntityAddCommand } from './add';
@@ -25,6 +26,14 @@ export const registerDevCommands = (program: Command): void => {
       dryRun?: boolean;
     },
   ) => {
+    if (options.dryRun && !options.once) {
+      console.warn(
+        chalk.yellow(
+          '--dry-run only applies with --once. Ignoring it; run `yarn twenty dev --once --dry-run` to preview changes.',
+        ),
+      );
+    }
+
     const commonOptions = {
       appPath: formatPath(appPath),
       verbose: options.verbose || options.debug,
@@ -56,7 +65,7 @@ export const registerDevCommands = (program: Command): void => {
       '--dry-run',
       'Preview the metadata changes without applying them (requires --once)',
     )
-    .option('--debounceMs <ms>', 'Debounce in ms (default: 2 000)')
+    .option('--debounceMs <ms>', 'Debounce in ms (default: 1 000)')
     .option('-v, --verbose', 'Show detailed logs')
     .option('-d, --debug', 'Show detailed logs (alias for --verbose)')
     .action(devAction);