fix(ui): remove overly strict pattern validation on postcard form

app/templates/postcard_form.html

@@ -6,7 +6,7 @@
 </div>
 <form method="post" action="{{ '/postcards/%d/edit' % postcard.id if postcard else '/profiles/%d/postcards' % profile.id }}" class="form-card">
     <label>编号 * <span style="font-weight:400;color:var(--text-muted);font-size:.8rem">格式：AB-1234567</span></label>
-    <input type="text" name="card_number" value="{{ postcard.card_number if postcard else '' }}" required pattern="[A-Za-z]{2}-\d{7}" title="两个字母 + 短横线 + 7位数字（如 AB-1234567）">
+    <input type="text" name="card_number" value="{{ postcard.card_number if postcard else '' }}" required placeholder="AB-1234567">
 
     <label>状态 *</label>
     <select name="status" id="status-select" onchange="toggleFields()" required>
@@ -19,7 +19,7 @@
         <label>收件人 *</label>
         <input type="text" name="recipient_name" value="{{ postcard.recipient_name if postcard else '' }}" required>
         <label>国家/地区 *</label>
-        <input type="text" name="country" value="{{ postcard.country if postcard else '' }}" required pattern="[A-Z]{2}" title="两个大写字母（如 JP、US）" maxlength="2" style="width:80px;text-transform:uppercase">
+        <input type="text" name="country" value="{{ postcard.country if postcard else '' }}" required maxlength="2" placeholder="JP" style="width:80px;text-transform:uppercase">
         <label>寄出时间 *</label>
         <input type="date" name="send_time" value="{{ postcard.send_time.strftime('%Y-%m-%d') if postcard and postcard.send_time else '' }}" required>
         <label>到达时间 *</label>