feat: 实现前端卡密管理界面

- 卡密列表展示与分页功能

- 单个/批量创建卡密

- 卡密删除与批量删除

- 卡密导出功能 (file-saver)

- 启用/禁用状态切换

- 状态判断 (有效/已使用/已失效)

- Toast 通知系统 (vue-sonner)

- 登录页面错误提示优化

- 后端登录错误消息中文化

backend/internal/repository/admin_repo.go

@@ -0,0 +1,120 @@
+package repository
+
+import (
+	"database/sql"
+	"time"
+
+	"gpt-manager-go/internal/models"
+)
+
+// AdminRepository 管理员仓储
+type AdminRepository struct {
+	db *sql.DB
+}
+
+// NewAdminRepository 创建管理员仓储
+func NewAdminRepository(db *sql.DB) *AdminRepository {
+	return &AdminRepository{db: db}
+}
+
+// FindByUsername 根据用户名查找管理员
+func (r *AdminRepository) FindByUsername(username string) (*models.Admin, error) {
+	admin := &models.Admin{}
+	err := r.db.QueryRow(`
+		SELECT id, username, email, password_hash, is_super_admin, is_active, created_at, last_login
+		FROM admins WHERE username = $1
+	`, username).Scan(
+		&admin.ID,
+		&admin.Username,
+		&admin.Email,
+		&admin.PasswordHash,
+		&admin.IsSuperAdmin,
+		&admin.IsActive,
+		&admin.CreatedAt,
+		&admin.LastLogin,
+	)
+
+	if err == sql.ErrNoRows {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	return admin, nil
+}
+
+// FindByEmail 根据邮箱查找管理员
+func (r *AdminRepository) FindByEmail(email string) (*models.Admin, error) {
+	admin := &models.Admin{}
+	err := r.db.QueryRow(`
+		SELECT id, username, email, password_hash, is_super_admin, is_active, created_at, last_login
+		FROM admins WHERE email = $1
+	`, email).Scan(
+		&admin.ID,
+		&admin.Username,
+		&admin.Email,
+		&admin.PasswordHash,
+		&admin.IsSuperAdmin,
+		&admin.IsActive,
+		&admin.CreatedAt,
+		&admin.LastLogin,
+	)
+
+	if err == sql.ErrNoRows {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	return admin, nil
+}
+
+// FindByID 根据 ID 查找管理员
+func (r *AdminRepository) FindByID(id int) (*models.Admin, error) {
+	admin := &models.Admin{}
+	err := r.db.QueryRow(`
+		SELECT id, username, email, password_hash, is_super_admin, is_active, created_at, last_login
+		FROM admins WHERE id = $1
+	`, id).Scan(
+		&admin.ID,
+		&admin.Username,
+		&admin.Email,
+		&admin.PasswordHash,
+		&admin.IsSuperAdmin,
+		&admin.IsActive,
+		&admin.CreatedAt,
+		&admin.LastLogin,
+	)
+
+	if err == sql.ErrNoRows {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	return admin, nil
+}
+
+// Create 创建管理员
+func (r *AdminRepository) Create(admin *models.Admin) error {
+	return r.db.QueryRow(`
+		INSERT INTO admins (username, email, password_hash, is_super_admin, is_active, created_at)
+		VALUES ($1, $2, $3, $4, $5, $6)
+		RETURNING id
+	`,
+		admin.Username,
+		admin.Email,
+		admin.PasswordHash,
+		admin.IsSuperAdmin,
+		admin.IsActive,
+		time.Now(),
+	).Scan(&admin.ID)
+}
+
+// UpdateLastLogin 更新最后登录时间
+func (r *AdminRepository) UpdateLastLogin(id int) error {
+	_, err := r.db.Exec(`
+		UPDATE admins SET last_login = $1 WHERE id = $2
+	`, time.Now(), id)
+	return err
+}