feat: 申诉常见理由快捷选择 + 证据截图上传

- 后端: 新增 appeal_reason_type, appeal_evidence_urls 字段
- 后端: 新建 upload_routes.py 图片上传接口
- 前端: history 页面添加快捷理由选择器 + 截图上传
- 前端: admin-review 页面展示证据图片 + 点击预览
- 新增 SQL 更新脚本 update_appeal_fields.sql

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

miniprogram/pages/history/index.wxml

@@ -61,7 +61,25 @@
       </view>
 
       <view wx:if="{{appealPostId === item.id}}">
-        <textarea class="textarea" placeholder="请输入申诉理由（至少 2 个字符）" value="{{appealReason}}" bindinput="onAppealInput" />
+        <view class="field">
+          <text class="field-label">申诉理由类型</text>
+          <picker mode="selector" range="{{appealReasonTypeOptions}}" range-key="label" value="{{appealReasonTypeIndex}}" bindchange="onReasonTypeChange">
+            <view class="picker-value">{{appealReasonTypeOptions[appealReasonTypeIndex].label}}</view>
+          </picker>
+        </view>
+        <textarea class="textarea" placeholder="可补充申诉理由（选择快捷理由后可省略）" value="{{appealReason}}" bindinput="onAppealInput" />
+        <view class="field">
+          <text class="field-label">证据截图（最多3张）</text>
+          <view class="evidence-grid">
+            <view class="evidence-item" wx:for="{{appealEvidenceFiles}}" wx:key="index">
+              <image class="evidence-thumb" src="{{item}}" mode="aspectFill" />
+              <view class="evidence-remove" data-index="{{index}}" bindtap="removeEvidence">×</view>
+            </view>
+            <view class="evidence-add" wx:if="{{appealEvidenceFiles.length < 3}}" bindtap="chooseEvidence">
+              <text class="evidence-add-icon">+</text>
+            </view>
+          </view>
+        </view>
         <view class="btn-row">
           <button class="btn btn-primary" bindtap="submitAppeal">提交申诉</button>
           <button class="btn btn-ghost" bindtap="cancelAppeal">取消</button>