Add mDNS hostname resolution

[Splat]

Consolidated from NEXT.md Phase 1.

Summary

Add an mDNS listener to resolve hostnames and attach them to observed peers.

Priority / Effort

• Priority: High
• Effort: Medium

Files

• lib/mdns_listener.go (new)
• lib/ndp_stats.go
• lib/display.go
• main.go

Implementation

• Add UDP listener for ff02::fb:5353 on the selected interface
• Parse AAAA and PTR response records
• Add hostname field to peer stats and render it in the TUI

Acceptance Criteria

• Hostnames appear for peers when mDNS data is observed
• Listener starts/stops with app lifecycle and does not block the TUI