feat: update DatePicker to handle date selection via onSelect callback in MediaFormModal

src/lib/DatePicker.svelte

@@ -3,14 +3,14 @@
   import { zhCN } from 'date-fns/locale';
   import { fade, scale } from 'svelte/transition';
 
-  let { value, placeholder = '选择日期' } = $props();
+  let { value, placeholder = '选择日期', onSelect } = $props();
   let isOpen = $state(false);
   let currentMonth = $state(value ? new Date(value) : new Date());
   let inputElement: HTMLInputElement;
 
   function handleSelect(date: Date) {
     const dateStr = format(date, 'yyyy-MM-dd');
-    value = dateStr;
+    onSelect(dateStr);
     isOpen = false;
   }
 

src/lib/MediaFormModal.svelte

@@ -109,6 +109,7 @@
           <label class="font-medium text-gray-700 whitespace-nowrap" for="date">日期</label>
           <DatePicker
             value={media.date}
+            onSelect={(date: string) => media.date = date}
             placeholder="选择日期"
           />
         </div>