fix: 优化日期选择器状态同步与日历列表渲染

src/lib/components/admin/DatePicker.svelte

@@ -9,22 +9,25 @@
 
 	let isOpen = $state(false);
 
-	let displayDate = $state(new Date());
+	let currentMonth = $state(new Date().getMonth());
+	let currentYear = $state(new Date().getFullYear());
 
 	$effect(() => {
-		if (value) {
-			const parsed = new Date(value);
-			if (!isNaN(parsed.getTime())) {
-				displayDate = parsed;
+		if (isOpen) {
+			if (value) {
+				const parsed = new Date(value);
+				if (!isNaN(parsed.getTime())) {
+					currentMonth = parsed.getMonth();
+					currentYear = parsed.getFullYear();
+				}
+			} else {
+				const now = new Date();
+				currentMonth = now.getMonth();
+				currentYear = now.getFullYear();
 			}
-		} else {
-			displayDate = new Date();
 		}
 	});
 
-	let currentMonth = $state(displayDate.getMonth());
-	let currentYear = $state(displayDate.getFullYear());
-
 	let container: HTMLDivElement;
 
 	function handleOutsideClick(e: MouseEvent) {
@@ -66,6 +69,9 @@
 	let daysInMonth = $derived(new Date(currentYear, currentMonth + 1, 0).getDate());
 	let firstDayOfWeek = $derived(new Date(currentYear, currentMonth, 1).getDay()); // 0 is Sunday
 
+	let emptyDays = $derived(Array.from({ length: firstDayOfWeek }).map((v, i) => i));
+	let monthDays = $derived(Array.from({ length: daysInMonth }).map((v, i) => i + 1));
+
 	const weekDays = ['日', '一', '二', '三', '四', '五', '六'];
 </script>
 
@@ -100,16 +106,15 @@
 			</div>
 
 			<div class="calendar-grid">
-				{#each weekDays as wd}
+				{#each weekDays as wd (wd)}
 					<div class="weekday">{wd}</div>
 				{/each}
 
-				{#each Array(firstDayOfWeek) as _}
+				{#each emptyDays as i (i)}
 					<div class="empty-day"></div>
 				{/each}
 
-				{#each Array(daysInMonth) as _, i}
-					{@const day = i + 1}
+				{#each monthDays as day (day)}
 					{@const isSelected =
 						value ===
 						`${currentYear}-${String(currentMonth + 1).padStart(2, '0')}-${String(day).padStart(2, '0')}`}