feat: 实现关注系统 + 通知侧边栏分类 TAB + 点赞聚合通知

- 新增关注系统：UserFollow 模型、FollowService（toggle/status/列表隐私控制）
- User 新增 FollowersCount/FollowingCount/FollowListPublic/NotifyPrefs 字段
- Space 页面增加四态关注按钮（关注/已关注/回关/已互粉）+ 粉丝/关注数链接
- 新增 /space/:uid/followers 和 /space/:uid/following 列表页
- 新增 NotifyFollow/NotifyLikeAggregated 通知类型
- ReactionService 点赞时写入 daily_like_summary，访问时生成聚合通知
- FollowService 关注时触发 NotifyFollow 通知
- 消息中心侧边栏升级为分类 TAB（全部/系统通知/@艾特/点赞/关注）
- NotificationService 新增 ListByCategory 按分类分页查询

internal/model/daily_like_summary.go

@@ -0,0 +1,14 @@
+package model
+
+import "time"
+
+// DailyLikeSummary 每日点赞汇聚（用于聚合点赞通知）
+type DailyLikeSummary struct {
+	ID         uint      `gorm:"primarykey" json:"id"`
+	AuthorUID  uint      `gorm:"uniqueIndex:idx_author_date;not null" json:"author_uid"` // 被点赞文章的作者
+	Date       string    `gorm:"type:varchar(10);uniqueIndex:idx_author_date;not null" json:"date"` // 日期 YYYY-MM-DD（Asia/Shanghai）
+	LikerUIDs  string    `gorm:"type:text" json:"liker_uids"`                                         // 点赞者 UID 列表（追加式，逗号分隔）
+	Notified   bool      `gorm:"default:false" json:"notified"`                                       // 是否已发送聚合通知
+	CreatedAt  time.Time `json:"created_at"`
+	UpdatedAt  time.Time `json:"updated_at"`
+}

internal/model/notification.go

@@ -2,13 +2,15 @@ package model
 
 // 消息/通知类型常量
 const (
-	NotifyAuditApproved  = "audit_approved"
-	NotifyAuditRejected  = "audit_rejected"
-	NotifyPostApproved   = "post_approved"
-	NotifyPostRejected   = "post_rejected"
-	NotifyLevelUp        = "level_up"
-	NotifyComment        = "comment"
-	NotifyCommentReply   = "comment_reply"
+	NotifyAuditApproved   = "audit_approved"
+	NotifyAuditRejected   = "audit_rejected"
+	NotifyPostApproved    = "post_approved"
+	NotifyPostRejected    = "post_rejected"
+	NotifyLevelUp         = "level_up"
+	NotifyComment         = "comment"
+	NotifyCommentReply    = "comment_reply"
+	NotifyLikeAggregated  = "like_aggregated" // 每日聚合点赞通知
+	NotifyFollow          = "follow"           // 关注通知
 )
 
 // Notification 消息/通知模型
@@ -26,13 +28,28 @@ type Notification struct {
 
 // NotifyTypeNames 通知类型 → 中文名
 var NotifyTypeNames = map[string]string{
-	NotifyAuditApproved: "资料审核",
-	NotifyAuditRejected: "资料审核",
-	NotifyPostApproved:  "稿件审核",
-	NotifyPostRejected:  "稿件审核",
-	NotifyLevelUp:       "等级提升",
-	NotifyComment:       "评论",
-	NotifyCommentReply:  "回复",
+	NotifyAuditApproved:  "资料审核",
+	NotifyAuditRejected:  "资料审核",
+	NotifyPostApproved:   "稿件审核",
+	NotifyPostRejected:   "稿件审核",
+	NotifyLevelUp:        "等级提升",
+	NotifyComment:        "评论",
+	NotifyCommentReply:   "回复",
+	NotifyLikeAggregated: "点赞",
+	NotifyFollow:         "关注",
+}
+
+// NotifyCategory 通知类型所属分类 TAB
+var NotifyCategory = map[string]string{
+	NotifyAuditApproved:  "system",
+	NotifyAuditRejected:  "system",
+	NotifyPostApproved:   "system",
+	NotifyPostRejected:   "system",
+	NotifyLevelUp:        "system",
+	NotifyComment:        "mention",
+	NotifyCommentReply:   "mention",
+	NotifyLikeAggregated: "like",
+	NotifyFollow:         "follow",
 }
 
 // NotificationListResult 消息列表查询结果

internal/model/user.go

@@ -19,6 +19,14 @@ type User struct {
 	Exp    int `gorm:"default:0" json:"exp"`    // 经验值（只增不减）
 	Energy int `gorm:"default:0" json:"energy"` // 域能余额（可为负数，乘10存储）
 
+	// 关注系统
+	FollowersCount   int  `gorm:"default:0" json:"followers_count"`     // 粉丝数（冗余计数器）
+	FollowingCount   int  `gorm:"default:0" json:"following_count"`     // 关注数（冗余计数器）
+	FollowListPublic bool `gorm:"default:true" json:"follow_list_public"` // 关注/粉丝列表是否公开
+
+	// 通知偏好 (JSON string)
+	NotifyPrefs string `gorm:"type:text;default:'{\"comment\":true,\"comment_reply\":true,\"like_aggregated\":true,\"follow\":true}'" json:"-"`
+
 	// 安全与审计
 	RegIP        string     `gorm:"type:varchar(45);default:''" json:"-"`        // 注册 IP
 	LastLoginIP  string     `gorm:"type:varchar(45);default:''" json:"-"`        // 最后登录 IP

internal/model/user_follow.go

@@ -0,0 +1,14 @@
+package model
+
+import "time"
+
+// UserFollow 关注关系
+type UserFollow struct {
+	FollowerID  uint      `gorm:"primaryKey;not null" json:"follower_id"`
+	FolloweeID  uint      `gorm:"primaryKey;not null" json:"followee_id"`
+	CreatedAt   time.Time `json:"created_at"`
+
+	// 联表查询填充（非数据库字段）
+	FollowerUsername string `gorm:"-:migration;<-:false;column:follower_username" json:"follower_username,omitempty"`
+	FolloweeUsername string `gorm:"-:migration;<-:false;column:followee_username" json:"followee_username,omitempty"`
+}