show trailing 12 months not calendar year

src/pages/index.tsx

@@ -36,10 +36,12 @@ export default function Home() {
     );
 
     const today = new Date();
-    const startOfYear = new Date(today.getFullYear(), 0, 1);
+    const startDate = new Date(today);
+    startDate.setMonth(today.getMonth() - 11);
+    startDate.setDate(1); // start from the first day of the month
 
     // generate daily data for each provider
-    for (let d = new Date(startOfYear); d <= today; d.setDate(d.getDate() + 1)) {
+    for (let d = new Date(startDate); d <= today; d.setDate(d.getDate() + 1)) {
       const dateString = d.toISOString().split('T')[0];
       
       Object.entries(PROVIDERS_MAP).forEach(([provider, { authors }]) => {