Improve apps (#19256)

- simplify the base application template
- remove --exhaustive option and replace by a --example option like in
next.js https://nextjs.org/docs/app/api-reference/cli
- Fix some bugs and logs
- add a post-card app in twenty-apps/examples/

packages/twenty-client-sdk/src/core/generated/index.ts

@@ -1,10 +1,15 @@
-// Stub — replaced at runtime by the generated client when the app
-// is installed on a Twenty instance or during `twenty app:dev`.
+// Stub — this file is replaced by the generated client when the app
+// is installed or sync on a Twenty instance.
+// Do not edit manually.
 export class CoreApiClient {
+  query: any;
+  mutation: any;
+  upload: any;
+
   constructor() {
     throw new Error(
       'CoreApiClient was not generated. ' +
-        'Install this app on a Twenty instance or run `twenty app:dev`.',
+        'Install this app on a Twenty instance or run `yarn twenty dev`.',
     );
   }
 }