Expose handlers list through the useNitroApp

Describe the feature

Hello, and thank you for your continued work on the open-source ecosystem — it's incredibly appreciated!

I’d like to propose exposing an additional API through useNitroApp that would allow access to the list of route handlers generated from the filesystem. This feature can be particularly useful when such metadata is needed on the client side.

For context, I received a request related to this functionality in one of my Nuxt modules. However, I couldn't find a clean way to implement it without extending Nitro itself.

Would you be open to this idea? I’ve created a draft PR to demonstrate the concept. If the approach makes sense, I’d be happy to clean it up — removing unnecessary playground files, adding proper test cases, and aligning with project conventions.

Alternatively, it might make more sense to implement this in the H3 layer. I know app.stack exists there, but it currently returns an empty array. If it’s more appropriate, I can explore that direction as well and expose the API via H3 instead.

Looking forward to hearing your thoughts!

Additional information

• Would you be willing to help implement this feature?

Start by examining the useNitroApp API and the H3 app.stack mentioned in the issue to determine which layer should expose route-handler metadata. Review the draft PR's approach if available. Done means the chosen API exposes the generated handler list for client-side metadata use, with proper tests and project conventions addressed.