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/handler/book.go

@@ -24,7 +24,8 @@ var excludeParts = []string{"序言", "尾声", "附录"}
 // 支持 excludeFixed=1：排除序言、尾声、附录（目录页固定模块，不参与中间篇章）
 func BookAllChapters(c *gin.Context) {
 	db := database.DB()
-	q := db.Model(&model.Chapter{})
+	q := db.Model(&model.Chapter{}).
+		Select("mid, id, part_id, part_title, chapter_id, chapter_title, section_title, word_count, is_free, price, sort_order, status, is_new, edition_standard, edition_premium, hot_score, created_at, updated_at")
 	if c.Query("excludeFixed") == "1" {
 		for _, p := range excludeParts {
 			q = q.Where("part_title NOT LIKE ?", "%"+p+"%")
@@ -430,7 +431,8 @@ func escapeLikeBook(s string) string {
 	return s
 }
 
-// BookSearch GET /api/book/search?q= 章节搜索（与 /api/search 逻辑一致）
+// BookSearch GET /api/book/search?q= 章节搜索
+// 优化：先搜标题（快），再搜内容（慢），不加载完整 content
 func BookSearch(c *gin.Context) {
 	q := strings.TrimSpace(c.Query("q"))
 	if q == "" {
@@ -438,26 +440,57 @@ func BookSearch(c *gin.Context) {
 		return
 	}
 	pattern := "%" + escapeLikeBook(q) + "%"
-	var list []model.Chapter
-	err := database.DB().Model(&model.Chapter{}).
-		Where("section_title LIKE ? OR content LIKE ?", pattern, pattern).
-		Order("sort_order ASC, id ASC").
-		Limit(20).
-		Find(&list).Error
-	if err != nil {
-		c.JSON(http.StatusOK, gin.H{"success": true, "results": []interface{}{}, "total": 0, "keyword": q})
-		return
+	db := database.DB()
+
+	type row struct {
+		ID           string `gorm:"column:id"`
+		MID          uint   `gorm:"column:mid"`
+		SectionTitle string `gorm:"column:section_title"`
+		PartTitle    string `gorm:"column:part_title"`
+		ChapterTitle string `gorm:"column:chapter_title"`
+		IsFree       *bool  `gorm:"column:is_free"`
 	}
-	lowerQ := strings.ToLower(q)
-	results := make([]gin.H, 0, len(list))
-	for _, ch := range list {
-		matchType := "content"
-		if strings.Contains(strings.ToLower(ch.SectionTitle), lowerQ) {
-			matchType = "title"
+
+	var titleHits []row
+	db.Model(&model.Chapter{}).
+		Select("id, mid, section_title, part_title, chapter_title, is_free").
+		Where("section_title LIKE ?", pattern).
+		Order("sort_order ASC, id ASC").
+		Limit(15).
+		Find(&titleHits)
+
+	titleIDs := make(map[string]bool, len(titleHits))
+	for _, h := range titleHits {
+		titleIDs[h.ID] = true
+	}
+
+	remaining := 20 - len(titleHits)
+	var contentHits []row
+	if remaining > 0 {
+		cq := db.Model(&model.Chapter{}).
+			Select("id, mid, section_title, part_title, chapter_title, is_free").
+			Where("content LIKE ?", pattern)
+		if len(titleIDs) > 0 {
+			ids := make([]string, 0, len(titleIDs))
+			for id := range titleIDs {
+				ids = append(ids, id)
+			}
+			cq = cq.Where("id NOT IN ?", ids)
 		}
+		cq.Order("sort_order ASC, id ASC").Limit(remaining).Find(&contentHits)
+	}
+
+	results := make([]gin.H, 0, len(titleHits)+len(contentHits))
+	for _, ch := range titleHits {
 		results = append(results, gin.H{
 			"id": ch.ID, "mid": ch.MID, "title": ch.SectionTitle, "part": ch.PartTitle, "chapter": ch.ChapterTitle,
-			"isFree": ch.IsFree, "matchType": matchType,
+			"isFree": ch.IsFree, "matchType": "title",
+		})
+	}
+	for _, ch := range contentHits {
+		results = append(results, gin.H{
+			"id": ch.ID, "mid": ch.MID, "title": ch.SectionTitle, "part": ch.PartTitle, "chapter": ch.ChapterTitle,
+			"isFree": ch.IsFree, "matchType": "content",
 		})
 	}
 	c.JSON(http.StatusOK, gin.H{"success": true, "results": results, "total": len(results), "keyword": q})