feat(auth): add Casbin RBAC and user activity tracking

Integrate Casbin for role-based access control with admin routes for role management. Add user activity logging service to track login and refresh events. Refactor audit service to use AI-based content moderation.

internal/model/role.go

@@ -0,0 +1,57 @@
+package model
+
+import "time"
+
+// Role 角色定义
+type Role struct {
+	ID          uint      `gorm:"primaryKey" json:"id"`
+	Name        string    `gorm:"uniqueIndex;size:64;not null" json:"name"`
+	DisplayName string    `gorm:"size:128;not null" json:"display_name"`
+	Description string    `json:"description"`
+	ParentRole  *string   `gorm:"size:64" json:"parent_role"`
+	Priority    int       `gorm:"default:0" json:"priority"`
+	CreatedAt   time.Time `json:"created_at"`
+	UpdatedAt   time.Time `json:"updated_at"`
+}
+
+func (Role) TableName() string {
+	return "roles"
+}
+
+// UserRole 用户角色关联
+type UserRole struct {
+	ID        uint      `gorm:"primaryKey" json:"id"`
+	UserID    string    `gorm:"index;size:64;not null" json:"user_id"`
+	Role      string    `gorm:"index;size:64;not null" json:"role"`
+	CreatedAt time.Time `json:"created_at"`
+	UpdatedAt time.Time `json:"updated_at"`
+}
+
+func (UserRole) TableName() string {
+	return "user_roles"
+}
+
+// CasbinRule Casbin 策略规则 (对应 casbin_rule 表)
+type CasbinRule struct {
+	ID    uint   `gorm:"primaryKey;autoIncrement"`
+	Ptype string `gorm:"size:255;not null;index"`
+	V0    string `gorm:"size:255;not null;index"`
+	V1    string `gorm:"size:255;not null;index"`
+	V2    string `gorm:"size:255;default:''"`
+	V3    string `gorm:"size:255;default:''"`
+	V4    string `gorm:"size:255;default:''"`
+	V5    string `gorm:"size:255;default:''"`
+}
+
+func (CasbinRule) TableName() string {
+	return "casbin_rule"
+}
+
+// 预定义角色常量
+const (
+	RoleSuperAdmin = "super_admin"
+	RoleAdmin      = "admin"
+	RoleModerator  = "moderator"
+	RoleUser       = "user"
+	RoleBanned     = "banned"
+)