feat: Integrate Firebase Cloud Messaging for push notifications; add service to handle token and message reception

app/src/main/java/com/rosetta/messenger/network/Packets.kt

@@ -452,3 +452,33 @@ class PacketChunk : Packet() {
         return stream
     }
 }
+
+/**
+ * Push Token packet (ID: 0x0A)
+ * Отправка FCM/APNS токена на сервер для push-уведомлений
+ */
+class PacketPushToken : Packet() {
+    var privateKey: String = ""
+    var publicKey: String = ""
+    var pushToken: String = ""
+    var platform: String = "android" // "android" или "ios"
+    
+    override fun getPacketId(): Int = 0x0A
+    
+    override fun receive(stream: Stream) {
+        privateKey = stream.readString()
+        publicKey = stream.readString()
+        pushToken = stream.readString()
+        platform = stream.readString()
+    }
+    
+    override fun send(): Stream {
+        val stream = Stream()
+        stream.writeInt16(getPacketId())
+        stream.writeString(privateKey)
+        stream.writeString(publicKey)
+        stream.writeString(pushToken)
+        stream.writeString(platform)
+        return stream
+    }
+}