feat: relay ping with RTT, server TOFU, lock icons (Phase 2 backport)

Rust JNI:
- nativePingRelay: QUIC connect with 3s timeout, returns RTT + server
  certificate fingerprint as JSON. Static method, no engine needed.

Kotlin:
- WzpEngine.pingRelay() static wrapper
- SettingsRepository: TOFU fingerprint persistence (tofu_{address} keys)
- CallViewModel: pingAllServers() coroutine, lockStatus() helper,
  PingResult/LockStatus data types
- InCallScreen: server chips show lock icon + RTT color (green/yellow),
  "Ping All" button

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

android/app/src/main/java/com/wzp/data/SettingsRepository.kt

@@ -29,6 +29,7 @@ class SettingsRepository(context: Context) {
         private const val KEY_IDENTITY_SEED = "identity_seed_hex"
         private const val KEY_AEC_ENABLED = "aec_enabled"
         private const val KEY_RECENT_ROOMS = "recent_rooms"
+        private const val TOFU_PREFIX = "tofu_"
     }
 
     // --- Servers ---
@@ -168,4 +169,14 @@ class SettingsRepository(context: Context) {
     fun clearRecentRooms() {
         prefs.edit().remove(KEY_RECENT_ROOMS).apply()
     }
+
+    // --- Server fingerprint TOFU ---
+
+    fun saveServerFingerprint(address: String, fingerprint: String) {
+        prefs.edit().putString("$TOFU_PREFIX$address", fingerprint).apply()
+    }
+
+    fun loadServerFingerprint(address: String): String? {
+        return prefs.getString("$TOFU_PREFIX$address", null)
+    }
 }