feat: integrate STOMP WebSocket and Agora VoIP signaling

walkguide-backend/demo/src/main/java/com/walkguide/config/WebSocketConfig.java

@@ -0,0 +1,46 @@
+package com.walkguide.config;
+
+import org.springframework.context.annotation.Configuration;
+import org.springframework.messaging.simp.config.MessageBrokerRegistry;
+import org.springframework.web.socket.config.annotation.EnableWebSocketMessageBroker;
+import org.springframework.web.socket.config.annotation.StompEndpointRegistry;
+import org.springframework.web.socket.config.annotation.WebSocketMessageBrokerConfigurer;
+
+/**
+ * Konfigurasi WebSocket dengan STOMP protocol.
+ *
+ * TOPIC vs QUEUE:
+ *   /topic/... → publish-subscribe (banyak subscriber, 1 publisher)
+ *   /queue/... → point-to-point (1 subscriber, 1 publisher)
+ *
+ * Topics yang digunakan:
+ *   Guardian subscribe: /topic/location/{userId}       ← live GPS user
+ *   Guardian subscribe: /queue/sos/{guardianId}        ← SOS alert
+ *   User subscribe:     /queue/notif/{userId}          ← notifikasi real-time
+ *
+ * Flutter (stomp_dart_client) connect ke: ws://{host}:{port}/ws
+ */
+@Configuration
+@EnableWebSocketMessageBroker
+public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
+
+    @Override
+    public void configureMessageBroker(MessageBrokerRegistry registry) {
+        // Prefix untuk topic/queue yang bisa di-subscribe client
+        registry.enableSimpleBroker("/topic", "/queue");
+
+        // Prefix untuk pesan yang dikirim dari client ke server (App destination)
+        // Flutter kirim ke /app/location → di-handle @MessageMapping("/location")
+        registry.setApplicationDestinationPrefixes("/app");
+    }
+
+    @Override
+    public void registerStompEndpoints(StompEndpointRegistry registry) {
+        // Endpoint WebSocket utama
+        // Flutter connect ke: ws://host:port/ws (tanpa SockJS)
+        // Browser/Postman bisa pakai SockJS fallback: http://host:port/ws
+        registry.addEndpoint("/ws")
+                .setAllowedOriginPatterns("*") // Allow semua origin untuk testing HP di LAN
+                .withSockJS();                  // SockJS fallback untuk browser compatibility
+    }
+}