Add LNURL-over-Nostr support (naddr + nprofile)

[Kukks]

Summary

Implements the LUD-XX: LNURL-over-Nostr specification, enabling LNURL flows over Nostr relays without requiring DNS or HTTPS infrastructure.

• ILNURLCommunicator transport abstraction in LNURL.Core — keeps Core free of Nostr/NNostr dependency
• NostrLNURLCommunicator with two addressing modes:
  • naddr (recommended): direct fetch of Kind 31120 parameterized replaceable events for static LNURL types (payRequest, channelRequest, withdrawRequest)
  • nprofile: NIP-17 Gift Wrap DM exchange for interactive types (login)
• LNURLNostrHelper: server-side helper for merchants — publishes Kind 31120 events, generates naddr/nprofile endpoints, handles incoming NIP-17 requests
• LNURLCompositeCommunicator: routes nostr: URIs to Nostr transport, everything else to HTTP
• Callback fallback: when service omits callback in Nostr response, defaults to original LNURL URI
• LUD-17 support: lnurlp:naddr1... and lnurlp:nprofile1... scheme URIs parse correctly
• NNostr.Client 0.0.54 with NIP-17 (Gift Wrap), NIP-44 (ChaCha20), NIP-59 support

Test plan

• 71 tests passing (13 new Nostr/communicator tests + 58 existing)
• naddr URI parsing, bech32 encoding, LUD-17 round-trip
• nprofile URI parsing and encoding
• LNURLNostrHelper naddr endpoint generation and Kind 31120 event creation
• Callback fallback for payRequest and withdrawRequest
• FetchInformation with ILNURLCommunicator (both HTTP and Nostr paths)

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 0a9aa55c-dad0-4f0c-a0d1-35e3edcd3db6

📥 Commits

Reviewing files that changed from the base of the PR and between 58fcdda and 0dba6a6.

📒 Files selected for processing (13)

• LNURL.Core/HttpLNURLCommunicator.cs
• LNURL.Core/ILNURLCommunicator.cs
• LNURL.Core/LNAuthRequest.cs
• LNURL.Core/LNURL.cs
• LNURL.Core/LNURLChannelRequest.cs
• LNURL.Core/LNURLPayRequest.cs
• LNURL.Core/LNURLWithdrawRequest.cs
• LNURL.Tests/UnitTest1.cs
• LNURL/LNURL.csproj
• LNURL/LNURLCompositeCommunicator.cs
• LNURL/LNURLNostrHelper.cs
• LNURL/NostrLNURLCommunicator.cs
• LNURL/TypeForwarders.cs

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch nostrpay

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