Enhance mini program environment configuration and chapter loading logic

- Introduced a debugging environment configuration in app.js, allowing for dynamic API endpoint selection based on the environment.
- Implemented lazy loading for chapter parts in chapters.js, improving performance by only fetching necessary data.
- Updated UI elements in chapters.wxml to reflect changes in chapter loading and added loading indicators.
- Enhanced error handling and data management for chapter retrieval, ensuring a smoother user experience.
- Added functionality for switching API environments in settings.js, visible only in development mode.

miniprogram/pages/my/my.wxml

@@ -154,7 +154,7 @@
         </view>
         <text class="menu-arrow">›</text>
       </view>
-      <view class="menu-item" wx:if="{{false}}" bindtap="handleMenuTap" data-id="settings">
+      <view class="menu-item" wx:if="{{showSettingsEntry}}" bindtap="handleMenuTap" data-id="settings">
         <view class="menu-left">
           <view class="menu-icon-wrap icon-gray"><image class="menu-icon-img" src="/assets/icons/settings-gray.svg" mode="aspectFit"/></view>
           <text class="menu-text">设置</text>