NIP-42 AUTH, DM reliability, relay picker, and profile enhancements

[barrydeen]

Summary

• NIP-42 AUTH: Full relay authentication flow — parse AUTH challenges, sign kind-22242 events, and automatically re-send DM subscriptions after auth completes
• NIP-44 fix: Correct HKDF key derivation to match spec (salt/ikm order in Extract, conversation key as PRK in Expand)
• DM reliability: Thread-safe DmRepository with synchronized access, gift wrap dedup for sent messages, send spinner UX, DM subscriptions sent to DM relays
• Relay picker: Replace flat list with scored relay board showing follow coverage counts, plus manual relay probe input with wss/ws fallback
• Profile enhancements: DM button on other users' profiles, lightning address display, rich content in bio, bare npub1 detection in RichContent
• UX cleanup: Remove new-DM FAB dialog in favor of profile-initiated conversations

Test plan

• Verify AUTH handshake works with relays that require it (e.g. relay.nostr.band)
• Send and receive DMs — confirm no duplicate messages on send
• Open relay picker and verify scored relays appear with coverage counts
• Probe a custom relay domain in the picker
• Check DM button appears on other users' profiles and navigates correctly
• Verify lightning address shows on profiles that have one
• Confirm bare npub1 mentions render as profile links in notes and bios