feat: add NIP-65 (Relay List Metadata) support #577

Pledge
N/A - I am planning to implement this myself.

Is your feature request related to a problem? Please describe.
Nostream currently lacks support for NIP-65 (Relay List Metadata). This leaves the DM relay routing incomplete from #458 - clients have no standard way to discover which relay to deliver messages to for a given user.

Describe the solution you'd like

• Accept and store kind:10002 replaceable events
• Advertise support in NIP-11 relay info document
• Completes the DM routing story from feat: implement NIP-17 & NIP-44 v2 for Modern Direct Messages #458

Describe alternatives you've considered
No real alternatives - NIP-65 is the standard way to solve relay discovery for DMs.

Additional context
Estimated: ~1 day.