feat: 首页发布增加发布类型选择（公开/私有/私信）

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

miniprogram/pages/home/index.wxml

@@ -10,10 +10,24 @@
 
     <view class="field">
       <text class="field-label">内容文本</text>
-      <textarea class="textarea" placeholder="请输入要发布的文本信息" value="{{text}}" bindinput="onInput" />
+      <textarea class="textarea" placeholder="请输入要发布的文本信息" value="{{text}}" data-field="text" bindinput="onInput" />
       <view class="field-help">当前字数：{{text.length}}，建议不少于 2 个字符。</view>
     </view>
 
+    <view class="field">
+      <view class="row">
+        <text class="field-label">发布类型</text>
+        <picker mode="selector" range="{{visibilityOptions}}" range-key="label" value="{{visibilityIndex}}" bindchange="onVisibilityChange">
+          <view class="picker-value">{{visibilityOptions[visibilityIndex].label}}</view>
+        </picker>
+      </view>
+    </view>
+
+    <view class="field" wx:if="{{visibility === 'direct'}}">
+      <text class="field-label">接收人用户名</text>
+      <input class="input" placeholder="私信发送时必填" value="{{recipientUsername}}" data-field="recipientUsername" bindinput="onInput" />
+    </view>
+
     <view class="field" wx:if="{{result}}">
       <text class="field-label">识别反馈</text>
       <view class="row">