feat: 内容管理第5批优化 - Bug修复 + 分享功能 + 代付功能

1. Bug修复：
   - 修复Markdown星号/下划线在小程序端原样显示问题（markdownToHtml增加__和_支持，contentParser增加Markdown格式剥离）
   - 修复@提及无反应（MentionSuggestion使用ref保持persons最新值，解决闭包捕获空数组问题）
   - 修复#链接标签点击"未找到小程序配置"（增加appId直接跳转降级路径）

2. 分享功能优化：
   - "分享到朋友圈"改为"分享给好友"（open-type从shareTimeline改为share）
   - 90%收益提示移到分享按钮下方
   - 阅读20%后向上滑动弹出分享浮层提示（4秒自动消失）

3. 代付功能：
   - 后端：新增UserBalance/BalanceTransaction/GiftUnlock三个模型
   - 后端：新增8个余额相关API（查询/充值/充值确认/代付/领取/退款/交易记录/礼物信息）
   - 小程序：阅读页新增"代付分享"按钮，支持用余额为好友解锁章节
   - 分享链接携带gift参数，好友打开自动领取解锁

Made-with: Cursor

soul-api/internal/router/router.go

@@ -79,6 +79,7 @@ func Setup(cfg *config.Config) *gin.Engine {
 			admin.GET("/author-settings", handler.AdminAuthorSettingsGet)
 			admin.POST("/author-settings", handler.AdminAuthorSettingsPost)
 			admin.PUT("/orders/refund", handler.AdminOrderRefund)
+			admin.POST("/content/upload", handler.AdminContentUpload)
 			admin.GET("/users", handler.AdminUsersList)
 			admin.POST("/users", handler.AdminUsersAction)
 			admin.PUT("/users", handler.AdminUsersAction)
@@ -278,6 +279,8 @@ func Setup(cfg *config.Config) *gin.Engine {
 			miniprogram.POST("/ckb/lead", handler.CKBLead)
 			miniprogram.POST("/ckb/index-lead", handler.CKBIndexLead)
 			miniprogram.POST("/upload", handler.UploadPost)
+			miniprogram.POST("/upload/image", handler.UploadImagePost)
+			miniprogram.POST("/upload/video", handler.UploadVideoPost)
 			miniprogram.DELETE("/upload", handler.UploadDelete)
 			miniprogram.GET("/user/addresses", handler.UserAddressesGet)
 			miniprogram.POST("/user/addresses", handler.UserAddressesPost)
@@ -310,6 +313,15 @@ func Setup(cfg *config.Config) *gin.Engine {
 			miniprogram.GET("/mentors/:id", handler.MiniprogramMentorsDetail)
 			miniprogram.POST("/mentors/:id/book", handler.MiniprogramMentorsBook)
 			miniprogram.GET("/about/author", handler.MiniprogramAboutAuthor)
+			// 余额与代付
+			miniprogram.GET("/balance", handler.BalanceGet)
+			miniprogram.POST("/balance/recharge", handler.BalanceRecharge)
+			miniprogram.POST("/balance/recharge/confirm", handler.BalanceRechargeConfirm)
+			miniprogram.POST("/balance/gift", handler.BalanceGift)
+			miniprogram.POST("/balance/gift/redeem", handler.BalanceGiftRedeem)
+			miniprogram.GET("/balance/gift/info", handler.BalanceGiftInfo)
+			miniprogram.POST("/balance/refund", handler.BalanceRefund)
+			miniprogram.GET("/balance/transactions", handler.BalanceTransactions)
 		}
 
 		// ----- 提现 -----