Android + web player: handle device_token authentication

Follows up on the security audit remediation (afbe113) which added
device_token auth to the WebSocket /device namespace.

Android player (ServerConfig.kt, WebSocketService.kt):
- Persist device_token in EncryptedSharedPreferences alongside device_id
- Send device_token in device:register on reconnect and playlist refresh
- Save/overwrite token from device:registered response (handles legacy
  devices getting their first token)
- Handle device:auth-error by clearing credentials and showing pairing screen
- clearDeviceCredentials() method wipes device_id, device_token, is_paired

Web player (player/index.html):
- Save deviceToken in localStorage config from device:registered response
- Send device_token in register() payload on reconnect
- Handle device:auth-error and device:unpaired events — clear config and
  show re-pair UI

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

android/app/src/main/java/com/remotedisplay/player/data/ServerConfig.kt

@@ -33,6 +33,10 @@ class ServerConfig(context: Context) {
         get() = prefs.getString("device_id", "") ?: ""
         set(value) = prefs.edit().putString("device_id", value).apply()
 
+    var deviceToken: String
+        get() = prefs.getString("device_token", "") ?: ""
+        set(value) = prefs.edit().putString("device_token", value).apply()
+
     var deviceName: String
         get() = prefs.getString("device_name", "Unnamed Display") ?: "Unnamed Display"
         set(value) = prefs.edit().putString("device_name", value).apply()
@@ -47,6 +51,14 @@ class ServerConfig(context: Context) {
         prefs.edit().putBoolean("is_paired", paired).apply()
     }
 
+    fun clearDeviceCredentials() {
+        prefs.edit()
+            .remove("device_id")
+            .remove("device_token")
+            .remove("is_paired")
+            .apply()
+    }
+
     fun clear() {
         prefs.edit().clear().apply()
     }

android/app/src/main/java/com/remotedisplay/player/service/WebSocketService.kt

@@ -102,15 +102,25 @@ class WebSocketService : Service() {
                     val data = args[0] as JSONObject
                     val newDeviceId = data.getString("device_id")
                     config.deviceId = newDeviceId
+                    // Persist device_token (issued on first register, or refreshed on reconnect)
+                    if (data.has("device_token")) {
+                        config.deviceToken = data.getString("device_token")
+                    }
                     Log.i("WebSocketService", "Registered as: $newDeviceId")
                     handler.post { onRegistered?.invoke(newDeviceId) }
                     startHeartbeat()
                 }
 
                 on("device:unpaired") {
-                    Log.w("WebSocketService", "Device not found on server - clearing config")
-                    config.setPaired(false)
-                    config.deviceId = ""
+                    Log.w("WebSocketService", "Device not found on server - clearing credentials")
+                    config.clearDeviceCredentials()
+                    handler.post { onUnpaired?.invoke() }
+                }
+
+                on("device:auth-error") { args ->
+                    val msg = (args.firstOrNull() as? JSONObject)?.optString("error", "Authentication failed") ?: "Authentication failed"
+                    Log.w("WebSocketService", "Device auth rejected: $msg — clearing credentials for re-pair")
+                    config.clearDeviceCredentials()
                     handler.post { onUnpaired?.invoke() }
                 }
 
@@ -234,6 +244,11 @@ class WebSocketService : Service() {
         val data = JSONObject().apply {
             if (config.isProvisioned && config.isPaired) {
                 put("device_id", config.deviceId)
+                // Send device_token for authentication (may be empty for legacy devices)
+                val token = config.deviceToken
+                if (token.isNotEmpty()) {
+                    put("device_token", token)
+                }
             } else {
                 // Generate a pairing code if we don't have one
                 val pairingCode = (100000..999999).random().toString()
@@ -279,6 +294,10 @@ class WebSocketService : Service() {
         // Re-register triggers the server to send current playlist
         val data = org.json.JSONObject().apply {
             put("device_id", config.deviceId)
+            val token = config.deviceToken
+            if (token.isNotEmpty()) {
+                put("device_token", token)
+            }
             put("device_info", deviceInfo.getDeviceInfo())
         }
         socket?.emit("device:register", data)

server/player/index.html

@@ -253,6 +253,7 @@
 
       socket.on('device:registered', (data) => {
         config.deviceId = data.device_id;
+        if (data.device_token) config.deviceToken = data.device_token;
         saveConfig(config);
         console.log('Registered:', data.device_id);
 
@@ -278,6 +279,30 @@
         showStatus('Waiting for content...');
       });
 
+      socket.on('device:unpaired', () => {
+        console.warn('Device not found on server — clearing credentials');
+        delete config.deviceId;
+        delete config.deviceToken;
+        config.paired = false;
+        saveConfig(config);
+        document.getElementById('setupScreen').style.display = 'flex';
+        document.getElementById('urlForm').style.display = 'block';
+        document.getElementById('pairingSection').style.display = 'none';
+        document.getElementById('setupStatus').textContent = 'Device was removed from server. Please reconnect.';
+      });
+
+      socket.on('device:auth-error', (data) => {
+        console.warn('Device auth rejected:', data?.error || 'unknown');
+        delete config.deviceId;
+        delete config.deviceToken;
+        config.paired = false;
+        saveConfig(config);
+        document.getElementById('setupScreen').style.display = 'flex';
+        document.getElementById('urlForm').style.display = 'block';
+        document.getElementById('pairingSection').style.display = 'none';
+        document.getElementById('setupStatus').textContent = 'Authentication failed. Please re-pair this device.';
+      });
+
       socket.on('device:playlist-update', (data) => {
         console.log('Playlist update:', data.assignments?.length, 'items');
         handlePlaylistUpdate(data);
@@ -361,6 +386,7 @@
       const data = {};
       if (config.deviceId && config.paired) {
         data.device_id = config.deviceId;
+        if (config.deviceToken) data.device_token = config.deviceToken;
       } else {
         const code = String(Math.floor(100000 + Math.random() * 900000));
         config.pairingCode = code;