Update settings application illustrations and app metadata previews (#19964)

## Summary
- Refresh the settings application visuals with new light/dark PNG
covers for the data model card
- Replace the custom and standard application carousel assets with the
new provided illustrations
- Align app chips, type tags, and application detail previews with the
updated icon and description treatment
- Keep the data model cover container and overlay button behavior intact
while swapping the underlying imagery

## Testing
- Not run (not requested)
- Existing frontend typecheck and formatting checks were exercised
during implementation

---------

Co-authored-by: Charles Bochet <charles@twenty.com>

packages/twenty-server/src/engine/core-modules/application/application.service.ts

@@ -354,7 +354,7 @@ export class ApplicationService {
 
     const workspaceCustomApplication = await this.create(
       {
-        description: 'Workspace custom application',
+        description: null,
         name: 'Custom',
         sourcePath: 'workspace-custom',
         version: '1.0.1',