feat(verification): add user identity verification system

Implement a complete user identity verification system with support for multiple identity types (student, teacher, staff, alumni). The system includes user-facing verification submission and status checking endpoints, admin endpoints for reviewing verification requests, middleware for protecting verification-required routes, and integration with the user model to track verification status.

internal/model/user.go

@@ -16,6 +16,28 @@ const (
 	UserStatusInactive UserStatus = "inactive"
 )
 
+// UserIdentity 用户身份类型
+type UserIdentity string
+
+const (
+	UserIdentityGeneral  UserIdentity = "general"  // 普通用户
+	UserIdentityStudent  UserIdentity = "student"  // 学生
+	UserIdentityTeacher  UserIdentity = "teacher"  // 教师
+	UserIdentityStaff    UserIdentity = "staff"    // 职工
+	UserIdentityAlumni   UserIdentity = "alumni"   // 校友
+	UserIdentityExternal UserIdentity = "external" // 外部人员
+)
+
+// VerificationStatus 审核状态
+type VerificationStatus string
+
+const (
+	VerificationStatusNotSubmitted VerificationStatus = "not_submitted" // 未提交
+	VerificationStatusPending      VerificationStatus = "pending"       // 审核中
+	VerificationStatusApproved     VerificationStatus = "approved"      // 已通过
+	VerificationStatusRejected     VerificationStatus = "rejected"      // 已拒绝
+)
+
 // User 用户实体
 type User struct {
 	ID            string  `json:"id" gorm:"type:varchar(36);primaryKey"`
@@ -42,6 +64,10 @@ type User struct {
 	FollowersCount int `json:"followers_count" gorm:"default:0"`
 	FollowingCount int `json:"following_count" gorm:"default:0"`
 
+	// 身份认证
+	Identity           UserIdentity       `json:"identity" gorm:"type:varchar(20);default:general"`
+	VerificationStatus VerificationStatus `json:"verification_status" gorm:"type:varchar(20);default:not_submitted"`
+
 	// 状态
 	Status      UserStatus `json:"status" gorm:"type:varchar(20);default:active"`
 	LastLoginAt *time.Time `json:"last_login_at" gorm:"type:timestamp"`