refactor: 优化文件存储路径逻辑，按年月进行分组归档

src/routes/admin/files/+page.server.ts

@@ -64,10 +64,12 @@ export const actions: Actions = {
 			return fail(400, { error: '没有提供有效的文件' });
 		}
 
-		// Generate unique key (timestamp + random string + original name)
+		// Generate unique key with year-month grouping (e.g. uploads/2026-07/timestamp-random.ext)
 		const ext = file.name.split('.').pop() || '';
 		const randomStr = Math.random().toString(36).substring(2, 8);
-		const key = `${Date.now()}-${randomStr}.${ext}`;
+		const now = new Date();
+		const yearMonth = `${now.getFullYear()}-${String(now.getMonth() + 1).padStart(2, '0')}`;
+		const key = `uploads/${yearMonth}/${Date.now()}-${randomStr}.${ext}`;
 
 		try {
 			// Upload to R2