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-server/src/engine/core-modules/application/application-manifest/application-sync.service.ts

@@ -52,10 +52,7 @@ export class ApplicationSyncService {
     hasSchemaMetadataChanged: boolean;
   }> {
     const ownerFlatApplication: FlatApplication = dryRun
-      ? await this.applicationService.findOneApplicationOrThrow({
-          universalIdentifier: manifest.application.universalIdentifier,
-          workspaceId,
-        })
+      ? await this.findInstalledApplicationOrThrow({ workspaceId, manifest })
       : await this.syncApplication({
           workspaceId,
           manifest,
@@ -77,6 +74,30 @@ export class ApplicationSyncService {
     return syncResult;
   }
 
+  private async findInstalledApplicationOrThrow({
+    workspaceId,
+    manifest,
+  }: {
+    workspaceId: string;
+    manifest: Manifest;
+  }): Promise<ApplicationEntity> {
+    const application = await this.applicationService.findByUniversalIdentifier(
+      {
+        universalIdentifier: manifest.application.universalIdentifier,
+        workspaceId,
+      },
+    );
+
+    if (!application) {
+      throw new ApplicationException(
+        `Application "${manifest.application.universalIdentifier}" is not installed in workspace "${workspaceId}". Install it first.`,
+        ApplicationExceptionCode.APP_NOT_INSTALLED,
+      );
+    }
+
+    return application;
+  }
+
   // Registers the application + only the pre-install logic function in
   // workspace metadata so the pre-install hook can resolve and execute it
   // before the main synchronizeFromManifest runs the full migrations.

packages/twenty-server/src/engine/core-modules/application/application-manifest/converters/from-logic-function-manifest-to-universal-flat-logic-function.util.ts

@@ -40,7 +40,7 @@ export const fromLogicFunctionManifestToUniversalFlatLogicFunction = ({
     workflowActionTriggerSettings:
       logicFunctionManifest.workflowActionTriggerSettings ?? null,
     isBuildUpToDate: true,
-    executionMode: LogicFunctionExecutionMode.PREBUILT,
+    executionMode: LogicFunctionExecutionMode.LIVE,
     createdAt: now,
     updatedAt: now,
     deletedAt: null,