feat: settings page with persistence, client alias in handshake, fix null fingerprints

- Add SettingsScreen with identity (alias, key backup/restore), audio defaults,
  server management, network prefs, and default room
- SettingsRepository persists all settings via SharedPreferences
- Auto-generate random display names on first launch (e.g. "Swift Wolf")
- Thread alias through CallOffer → relay handshake → RoomUpdate broadcast
- Derive caller fingerprint from identity key in relay handshake (fixes null
  fingerprints when --auth-url is not set)
- Persist identity seed for stable fingerprints across reconnects
- Add alias field to SignalMessage::CallOffer (serde default for backward compat)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/wzp-client/src/cli.rs

@@ -287,6 +287,7 @@ async fn main() -> anyhow::Result<()> {
     let _crypto_session = wzp_client::handshake::perform_handshake(
         &*transport,
         &seed.0,
+        None, // alias — desktop client doesn't set one yet
     ).await?;
     info!("crypto handshake complete");
 

crates/wzp-client/src/handshake.rs

@@ -17,6 +17,7 @@ use wzp_proto::{MediaTransport, QualityProfile, SignalMessage};
 pub async fn perform_handshake(
     transport: &dyn MediaTransport,
     seed: &[u8; 32],
+    alias: Option<&str>,
 ) -> Result<Box<dyn CryptoSession>, anyhow::Error> {
     // 1. Create key exchange from identity seed
     let mut kx = WarzoneKeyExchange::from_identity_seed(seed);
@@ -41,6 +42,7 @@ pub async fn perform_handshake(
             QualityProfile::DEGRADED,
             QualityProfile::CATASTROPHIC,
         ],
+        alias: alias.map(|s| s.to_string()),
     };
     transport.send_signal(&offer).await?;