feat(nip86): implement WebSocket relay management API

[Ferryx349]

Context & Problem

Currently, Nostream operators must manage the relay either via SSH or the built-in HTTP Admin Console. However, standard Nostr admin clients cannot interact with Nostream natively over WebSockets, breaking interoperability for operators who want to use generic ecosystem tools.

Proposed Solution

Implement NIP-86 to support standardized WebSocket RPC commands for relay administration.

Scope

• Auth: Verify incoming ["admin", ...] messages against the configured relay operator's pubkey.
• Commands: Implement handlers for core commands such as banning pubkeys, unbanning, deleting events, and querying relay status.
• Database Integration: Connect the NIP-86 command handlers directly to the existing database repository functions being built for the HTTP Admin Console.

NIPs Involved: NIP-86