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/dto/dto.go

@@ -44,6 +44,8 @@ type UserSelfResponse struct {
 	FollowingCount int     `json:"following_count"`
 	IsVerified     bool    `json:"is_verified"`
 	CreatedAt      string  `json:"created_at"`
+	// 隐私设置
+	PrivacySettings *PrivacySettingsResponse `json:"privacy_settings,omitempty"`
 }
 
 // UserDetailResponse 用户详情响应（仅本人可见，包含敏感信息）
@@ -66,6 +68,8 @@ type UserDetailResponse struct {
 	IsFollowing    bool    `json:"is_following"`
 	IsFollowingMe  bool    `json:"is_following_me"`
 	CreatedAt      string  `json:"created_at"`
+	// 隐私设置
+	PrivacySettings *PrivacySettingsResponse `json:"privacy_settings,omitempty"`
 }
 
 // ==================== Admin User DTOs ====================
@@ -1403,3 +1407,33 @@ type AdminReviewVerificationRequest struct {
 	Approve      bool   `json:"approve" binding:"required"`
 	RejectReason string `json:"reject_reason" binding:"omitempty,max=500"`
 }
+
+// ==================== Privacy & Account Deletion DTOs ====================
+
+// PrivacySettingsRequest 隐私设置请求
+type PrivacySettingsRequest struct {
+	FollowersVisibility *string `json:"followers_visibility" binding:"omitempty,oneof=everyone following self"`
+	FollowingVisibility *string `json:"following_visibility" binding:"omitempty,oneof=everyone following self"`
+	PostsVisibility     *string `json:"posts_visibility" binding:"omitempty,oneof=everyone following self"`
+	FavoritesVisibility *string `json:"favorites_visibility" binding:"omitempty,oneof=everyone following self"`
+}
+
+// PrivacySettingsResponse 隐私设置响应
+type PrivacySettingsResponse struct {
+	FollowersVisibility string `json:"followers_visibility"`
+	FollowingVisibility string `json:"following_visibility"`
+	PostsVisibility     string `json:"posts_visibility"`
+	FavoritesVisibility string `json:"favorites_visibility"`
+}
+
+// RequestDeletionRequest 申请注销请求
+type RequestDeletionRequest struct {
+	Password string `json:"password" binding:"required"`
+}
+
+// DeletionStatusResponse 注销状态响应
+type DeletionStatusResponse struct {
+	IsPendingDeletion   bool   `json:"is_pending_deletion"`
+	DeletionRequestedAt string `json:"deletion_requested_at,omitempty"`
+	CoolDownDays        int    `json:"cool_down_days,omitempty"`
+}