feat: montly songs

src/utils/monthKey.js

@@ -0,0 +1,9 @@
+export const buildMonthKey = (date = new Date()) => {
+  const target = date instanceof Date ? new Date(date) : new Date()
+  const year = target.getFullYear()
+  const month = String(target.getMonth() + 1).padStart(2, '0')
+
+  return `${year}-${month}`
+}
+
+export default buildMonthKey