feat(privacy): add user privacy settings and account deletion system

Add privacy settings allowing users to control visibility of their followers, following, posts, and favorites lists with three visibility levels: everyone, following, and self. Also implement account deletion workflow with 30-day cooldown period.

- Add PrivacySettings model with visibility levels
- Add DTOs for privacy settings and account deletion
- Add repository methods for privacy settings and deletion
- Add service methods to check visibility permissions
- Add handlers for get/update privacy settings and account deletion
- Add new routes for privacy settings and account management
- Add account cleanup service for hard-deleting expired accounts
- Modify login to cancel deletion when user logs in

BREAKING CHANGE: Users with pending_deletion status can no longer log in; logging in now automatically cancels deletion requests.

internal/model/user.go

@@ -11,11 +11,29 @@ import (
 type UserStatus string
 
 const (
-	UserStatusActive   UserStatus = "active"
-	UserStatusBanned   UserStatus = "banned"
-	UserStatusInactive UserStatus = "inactive"
+	UserStatusActive          UserStatus = "active"
+	UserStatusBanned          UserStatus = "banned"
+	UserStatusInactive        UserStatus = "inactive"
+	UserStatusPendingDeletion UserStatus = "pending_deletion"
 )
 
+// VisibilityLevel 可见性级别
+type VisibilityLevel string
+
+const (
+	VisibilityEveryone  VisibilityLevel = "everyone"
+	VisibilityFollowing VisibilityLevel = "following"
+	VisibilitySelf      VisibilityLevel = "self"
+)
+
+// PrivacySettings 隐私设置
+type PrivacySettings struct {
+	FollowersVisibility VisibilityLevel `json:"followers_visibility" gorm:"type:varchar(20);default:everyone"`
+	FollowingVisibility VisibilityLevel `json:"following_visibility" gorm:"type:varchar(20);default:everyone"`
+	PostsVisibility     VisibilityLevel `json:"posts_visibility" gorm:"type:varchar(20);default:everyone"`
+	FavoritesVisibility VisibilityLevel `json:"favorites_visibility" gorm:"type:varchar(20);default:everyone"`
+}
+
 // UserIdentity 用户身份类型
 type UserIdentity string
 
@@ -73,6 +91,12 @@ type User struct {
 	LastLoginAt *time.Time `json:"last_login_at" gorm:"type:timestamp"`
 	LastLoginIP string     `json:"last_login_ip" gorm:"type:varchar(45)"`
 
+	// 账号注销
+	DeletionRequestedAt *time.Time `json:"deletion_requested_at" gorm:"type:timestamp"`
+
+	// 隐私设置
+	PrivacySettings PrivacySettings `json:"privacy_settings" gorm:"embedded;embeddedPrefix:privacy_"`
+
 	// 时间戳
 	CreatedAt time.Time      `json:"created_at" gorm:"autoCreateTime"`
 	UpdatedAt time.Time      `json:"updated_at" gorm:"autoUpdateTime"`