feat(server): integrate ip ban cron and refine updates

- Initialize and schedule IP ban maintenance tasks in server entry point
- Perform initial IP ban sync to Redis on startup
- Implement optional JSON unmarshalling to handle null `expires_at` in API
- Add CIDR overlap validation when updating rule status to active

internal/service/ip_ban.go

@@ -15,10 +15,10 @@ import (
 )
 
 var (
-	ErrInvalidCIDR     = errors.New("invalid CIDR format")
-	ErrCIDROverlap     = errors.New("CIDR overlaps with existing active rule")
-	ErrIPBanNotFound   = errors.New("IP ban not found")
-	ErrDuplicateCIDR   = errors.New("CIDR already exists")
+	ErrInvalidCIDR   = errors.New("invalid CIDR format")
+	ErrCIDROverlap   = errors.New("CIDR overlaps with existing active rule")
+	ErrIPBanNotFound = errors.New("IP ban not found")
+	ErrDuplicateCIDR = errors.New("CIDR already exists")
 )
 
 // IPBanService handles global IP ban operations.
@@ -93,9 +93,10 @@ type CreateIPBanRequest struct {
 
 // UpdateIPBanRequest represents a request to update an IP ban.
 type UpdateIPBanRequest struct {
-	Reason    *string `json:"reason,omitempty"`
-	ExpiresAt *int64  `json:"expires_at,omitempty"` // Use pointer to distinguish between "not set" and "set to null"
-	Status    *string `json:"status,omitempty"`
+	Reason       *string `json:"reason,omitempty"`
+	ExpiresAt    *int64  `json:"expires_at,omitempty"`
+	ExpiresAtSet bool    `json:"-"`
+	Status       *string `json:"status,omitempty"`
 }
 
 // Create creates a new IP ban with validation.
@@ -180,11 +181,25 @@ func (s *IPBanService) Update(ctx context.Context, id uint, req UpdateIPBanReque
 		return nil, err
 	}
 
+	if req.Status != nil && *req.Status == model.IPBanStatusActive && ban.Status != model.IPBanStatusActive {
+		var activeRules []model.IPBan
+		if err := s.db.WithContext(ctx).
+			Where("status = ? AND id <> ?", model.IPBanStatusActive, ban.ID).
+			Find(&activeRules).Error; err != nil {
+			return nil, err
+		}
+		for _, rule := range activeRules {
+			if CIDROverlaps(ban.CIDR, rule.CIDR) {
+				return nil, fmt.Errorf("%w: overlaps with %s", ErrCIDROverlap, rule.CIDR)
+			}
+		}
+	}
+
 	updates := make(map[string]interface{})
 	if req.Reason != nil {
 		updates["reason"] = *req.Reason
 	}
-	if req.ExpiresAt != nil {
+	if req.ExpiresAtSet {
 		updates["expires_at"] = req.ExpiresAt
 	}
 	if req.Status != nil {