fix: 修复 mp-weixin 模板箭头函数和 TextDecoder 不兼容

- 微信小程序 wxml 模板不支持内联箭头函数
  @submit 改为方法引用，submitClarification 自己找未提交卡片
- TextDecoder 在 mp-weixin 不可用
  decodeChunk 改用纯 JS UTF-8 解码实现

mini-program/src/pages/main/ScriptView.vue

@@ -126,7 +126,7 @@
                 <ClarificationCard
                   v-if="!msg.submitted && msg.card"
                   :card="msg.card"
-                  @submit="(answer) => submitClarification(msg, answer)"
+                  @submit="submitClarification"
                 />
                 <view v-else class="card-answered">
                   <text>已回答：{{ msg.answer }}</text>
@@ -1674,11 +1674,13 @@ const handleShortNovelEvent = (event) => {
   }
 }
 
-const submitClarification = (msg, answer) => {
+const submitClarification = (answer) => {
   if (answeringClarification.value) return
-  if (msg) {
-    msg.submitted = true
-    msg.answer = answer
+  // 找最后一张未提交的卡片消息（mp-weixin 模板不支持内联箭头函数传 msg，改为自己查找）
+  const card = [...resultMessages.value].reverse().find(m => m.kind === 'card' && !m.submitted)
+  if (card) {
+    card.submitted = true
+    card.answer = answer
   }
   addResultMessage({ role: 'user', kind: 'text', content: answer })
   answeringClarification.value = true