Add new app with endpoint for submitting labels

[djstrong]

Create a new app module with an API endpoint that accepts:

• a list of labels
• a caller address

The endpoint should:

1. Validate incoming labels and check for any unknown labels (use ENSApi).
2. For now, store/log all submitted labels along with the caller address.
3. Prepare for future functionality where:
   • Labels will be emitted on-chain.
   • Emission should be batched for optimization (not per-request, e.g. every hour).
4. Store or structure the caller address data in a way that enables building a leaderboard feature later.