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/api/ip_ban_handler.go

@@ -1,6 +1,7 @@
 package api
 
 import (
+	"encoding/json"
 	"errors"
 	"net/http"
 	"strconv"
@@ -29,9 +30,9 @@ 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"`
-	Status    *string `json:"status,omitempty"`
+	Reason    *string       `json:"reason,omitempty"`
+	ExpiresAt optionalInt64 `json:"expires_at,omitempty"`
+	Status    *string       `json:"status,omitempty"`
 }
 
 // IPBanView represents the API response for an IP ban.
@@ -47,6 +48,25 @@ type IPBanView struct {
 	UpdatedAt int64  `json:"updated_at"`
 }
 
+type optionalInt64 struct {
+	Value *int64
+	Set   bool
+}
+
+func (o *optionalInt64) UnmarshalJSON(data []byte) error {
+	o.Set = true
+	if string(data) == "null" {
+		o.Value = nil
+		return nil
+	}
+	var v int64
+	if err := json.Unmarshal(data, &v); err != nil {
+		return err
+	}
+	o.Value = &v
+	return nil
+}
+
 func toIPBanView(ban *model.IPBan) IPBanView {
 	return IPBanView{
 		ID:        ban.ID,
@@ -183,6 +203,7 @@ func (h *IPBanHandler) Get(c *gin.Context) {
 // @Success      200  {object}  IPBanView
 // @Failure      400  {object}  gin.H
 // @Failure      404  {object}  gin.H
+// @Failure      409  {object}  gin.H
 // @Failure      500  {object}  gin.H
 // @Router       /admin/ip-bans/{id} [put]
 func (h *IPBanHandler) Update(c *gin.Context) {
@@ -199,15 +220,19 @@ func (h *IPBanHandler) Update(c *gin.Context) {
 	}
 
 	ban, err := h.ipBanService.Update(c.Request.Context(), uint(id), service.UpdateIPBanRequest{
-		Reason:    req.Reason,
-		ExpiresAt: req.ExpiresAt,
-		Status:    req.Status,
+		Reason:       req.Reason,
+		ExpiresAt:    req.ExpiresAt.Value,
+		ExpiresAtSet: req.ExpiresAt.Set,
+		Status:       req.Status,
 	})
 
 	if err != nil {
-		if errors.Is(err, service.ErrIPBanNotFound) {
+		switch {
+		case errors.Is(err, service.ErrIPBanNotFound):
 			c.JSON(http.StatusNotFound, gin.H{"error": "IP ban not found"})
-		} else {
+		case errors.Is(err, service.ErrCIDROverlap):
+			c.JSON(http.StatusConflict, gin.H{"error": err.Error()})
+		default:
 			c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to update IP ban", "details": err.Error()})
 		}
 		return