Added frontend

backend/app/middleware/api_host_guard.go

@@ -0,0 +1,12 @@
+package middleware
+
+import "github.com/gofiber/fiber/v3"
+
+func APIHostGuard(allowedHost string) fiber.Handler {
+	return func(c fiber.Ctx) error {
+		if c.Hostname() != allowedHost {
+			return c.Status(fiber.StatusNotFound).SendString("Not Found")
+		}
+		return c.Next()
+	}
+}