feat(auth): enhance security with token hashing and sync integration

- Add token hash fields to Master and Key models for indexed lookups
- Implement SyncService integration in admin and master handlers
- Update master key validation with backward-compatible digest lookup
- Hash child keys in database and store token digests for Redis sync
- Add master metadata sync to Redis for balancer validation
- Ensure backward compatibility with legacy rows during migration

internal/api/master_handler.go

@@ -11,10 +11,11 @@ import (
 
 type MasterHandler struct {
 	masterService *service.MasterService
+	syncService   *service.SyncService
 }
 
-func NewMasterHandler(masterService *service.MasterService) *MasterHandler {
-	return &MasterHandler{masterService: masterService}
+func NewMasterHandler(masterService *service.MasterService, syncService *service.SyncService) *MasterHandler {
+	return &MasterHandler{masterService: masterService, syncService: syncService}
 }
 
 type IssueChildKeyRequest struct {
@@ -55,6 +56,11 @@ func (h *MasterHandler) IssueChildKey(c *gin.Context) {
 		return
 	}
 
+	if err := h.syncService.SyncKey(key); err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to sync child key", "details": err.Error()})
+		return
+	}
+
 	c.JSON(http.StatusCreated, gin.H{
 		"id":         key.ID,
 		"key_secret": rawChildKey,