feat(server): add apple-itunes-app meta tag on shage page (#13065)

disable on selfhosted

close AF-2715

![IMG_1232](https://github.com/user-attachments/assets/21fdd066-3f67-411e-9407-7349e221c23e)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Added an Apple iTunes app association meta tag to the document share
page for improved app integration, shown only in non-self-hosted
environments.

* **Tests**
* Introduced end-to-end tests to verify the conditional presence of the
Apple iTunes app meta tag based on the deployment environment.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->


#### PR Dependency Tree


* **PR #13065** 👈

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

packages/backend/server/src/core/doc-renderer/controller.ts

@@ -171,6 +171,7 @@ export class DocRendererController {
       name="apple-mobile-web-app-status-bar-style"
       content="black-translucent"
     />
+    ${env.selfhosted ? '' : '<meta name="apple-itunes-app" content="app-id=6736937980" />'}
 
     <title>${title}</title>
     <meta name="theme-color" content="#fafafa" />