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/settings/settings.js

@@ -14,6 +14,8 @@ Page({
     
     // 切换账号（开发）
     showSwitchAccountModal: false,
+    // 调试环境：当前 API 环境标签
+    apiEnvLabel: '自动',
     switchAccountUserId: '',
     switchAccountLoading: false,
     
@@ -36,17 +38,30 @@ Page({
     wx.showShareMenu({ withShareTimeline: true })
     const accountInfo = wx.getAccountInfoSync ? wx.getAccountInfoSync() : null
     const envVersion = accountInfo?.miniProgram?.envVersion || ''
+    const envInfo = app.getDebugEnvInfo()
     this.setData({
       statusBarHeight: app.globalData.statusBarHeight,
       isLoggedIn: app.globalData.isLoggedIn,
       userInfo: app.globalData.userInfo,
-      isDevMode: envVersion === 'develop'
+      isDevMode: envVersion === 'develop',
+      apiEnvLabel: envInfo.label
     })
     this.loadBindingInfo()
   },
 
   onShow() {
     this.loadBindingInfo()
+    if (this.data.isDevMode) {
+      const envInfo = getApp().getDebugEnvInfo()
+      this.setData({ apiEnvLabel: envInfo.label })
+    }
+  },
+
+  // 一键切换 API 环境（开发版）
+  switchApiEnv() {
+    const next = getApp().switchDebugEnv()
+    this.setData({ apiEnvLabel: next.label })
+    wx.showToast({ title: `已切到 ${next.label}`, icon: 'none' })
   },
 
   // 加载绑定信息