Added backend dockerfile

backend/go.mod

@@ -0,0 +1,3 @@
+module backend
+
+go 1.24.4

backend/main.go

@@ -0,0 +1,11 @@
+package main
+
+import "time"
+
+func main() {
+	println("Hello, world!")
+
+	for {
+		time.Sleep(1 * time.Second)
+	}
+}