docs: add transport and tx-prover endpoint references

## Summary

Document the following active service endpoints and status pages used in client configuration:

### Service endpoints

- **Transport layer:** `https://transport.miden.io` — private note transport endpoint
- **Delegated prover:** `https://tx-prover.testnet.miden.io/` — remote transaction proving endpoint

These are API endpoints (not web pages) that users need for client setup. Currently undocumented.

### Status pages

- **Testnet:** https://status.testnet.miden.io/
- **Devnet:** https://status.devnet.miden.io/

### Suggested locations

- Client setup / configuration guide
- Network infrastructure reference (if exists)