Add remote stream relay feature: relay remote DJ streams to listeners

- Server-side: Added remote URL support in ffmpeg transcoder
- UI: Added relay controls in streaming panel with URL input
- Client: Added start/stop relay functions with socket communication
- Listener: Shows remote relay status in stream indicator

index.html

@@ -398,6 +398,16 @@
                     <span class="quality-hint">Lower = more stable on poor connections</span>
                 </div>
             </div>
+
+            <div class="remote-relay-section">
+                <h4>🔗 Remote Stream Relay</h4>
+                <div class="relay-controls">
+                    <input type="text" id="remote-stream-url" placeholder="Paste remote stream URL (e.g., http://remote.dj/stream.mp3)" class="relay-url-input">
+                    <button class="relay-btn" id="start-relay-btn" onclick="startRemoteRelay()">START RELAY</button>
+                    <button class="relay-btn stop" id="stop-relay-btn" onclick="stopRemoteRelay()" style="display: none;">STOP RELAY</button>
+                </div>
+                <div class="relay-status" id="relay-status"></div>
+            </div>
         </div>
     </div>