NIP-46 bunker mode (desktop)

[kwsantiago]

Android has a full NIP-46 remote signing service (Nostr Connect bunker). Desktop has nothing.

Android parity features needed:

• Start/stop bunker service
• Generate bunker connection URL (bunker://...)
• Display bunker URL as QR code for client pairing
• Relay configuration for bunker (separate from FROST relays)
• View authorized clients list
• Revoke individual clients
• Revoke all clients
• Request approval UI for incoming NIP-46 operations (sign, encrypt, decrypt, get_public_key)

Implementation notes:

• Uses keep-nip46 crate for the protocol
• Needs relay management UI (Relay management UI (desktop) #194) for bunker relay config
• Approval screen should show: method name, event kind, event content, app info