feat: 完成B端认证系统和商户管理模块测试补全

主要变更：
- 新增B端认证系统（后台+H5）：登录、登出、Token刷新、密码修改
- 完善商户管理和商户账号管理功能
- 补全单元测试（ShopService: 72.5%, ShopAccountService: 79.8%）
- 新增集成测试（商户管理+商户账号管理）
- 归档OpenSpec提案（add-shop-account-management, implement-b-end-auth-system）
- 完善文档（使用指南、API文档、认证架构说明）

测试统计：
- 13个测试套件，37个测试用例，100%通过率
- 平均覆盖率76.2%，达标

OpenSpec验证：通过（strict模式）

internal/handler/admin/shop_account.go

@@ -0,0 +1,103 @@
+package admin
+
+import (
+	"strconv"
+
+	"github.com/gofiber/fiber/v2"
+
+	"github.com/break/junhong_cmp_fiber/internal/model"
+	shopAccountService "github.com/break/junhong_cmp_fiber/internal/service/shop_account"
+	"github.com/break/junhong_cmp_fiber/pkg/errors"
+	"github.com/break/junhong_cmp_fiber/pkg/response"
+)
+
+type ShopAccountHandler struct {
+	service *shopAccountService.Service
+}
+
+func NewShopAccountHandler(service *shopAccountService.Service) *ShopAccountHandler {
+	return &ShopAccountHandler{service: service}
+}
+
+func (h *ShopAccountHandler) List(c *fiber.Ctx) error {
+	var req model.ShopAccountListRequest
+	if err := c.QueryParser(&req); err != nil {
+		return errors.New(errors.CodeInvalidParam, "请求参数解析失败")
+	}
+
+	accounts, total, err := h.service.List(c.UserContext(), &req)
+	if err != nil {
+		return err
+	}
+
+	return response.SuccessWithPagination(c, accounts, total, req.Page, req.PageSize)
+}
+
+func (h *ShopAccountHandler) Create(c *fiber.Ctx) error {
+	var req model.CreateShopAccountRequest
+	if err := c.BodyParser(&req); err != nil {
+		return errors.New(errors.CodeInvalidParam, "请求参数解析失败")
+	}
+
+	account, err := h.service.Create(c.UserContext(), &req)
+	if err != nil {
+		return err
+	}
+
+	return response.Success(c, account)
+}
+
+func (h *ShopAccountHandler) Update(c *fiber.Ctx) error {
+	id, err := strconv.ParseUint(c.Params("id"), 10, 64)
+	if err != nil {
+		return errors.New(errors.CodeInvalidParam, "无效的账号 ID")
+	}
+
+	var req model.UpdateShopAccountRequest
+	if err := c.BodyParser(&req); err != nil {
+		return errors.New(errors.CodeInvalidParam, "请求参数解析失败")
+	}
+
+	account, err := h.service.Update(c.UserContext(), uint(id), &req)
+	if err != nil {
+		return err
+	}
+
+	return response.Success(c, account)
+}
+
+func (h *ShopAccountHandler) UpdatePassword(c *fiber.Ctx) error {
+	id, err := strconv.ParseUint(c.Params("id"), 10, 64)
+	if err != nil {
+		return errors.New(errors.CodeInvalidParam, "无效的账号 ID")
+	}
+
+	var req model.UpdateShopAccountPasswordRequest
+	if err := c.BodyParser(&req); err != nil {
+		return errors.New(errors.CodeInvalidParam, "请求参数解析失败")
+	}
+
+	if err := h.service.UpdatePassword(c.UserContext(), uint(id), &req); err != nil {
+		return err
+	}
+
+	return response.Success(c, nil)
+}
+
+func (h *ShopAccountHandler) UpdateStatus(c *fiber.Ctx) error {
+	id, err := strconv.ParseUint(c.Params("id"), 10, 64)
+	if err != nil {
+		return errors.New(errors.CodeInvalidParam, "无效的账号 ID")
+	}
+
+	var req model.UpdateShopAccountStatusRequest
+	if err := c.BodyParser(&req); err != nil {
+		return errors.New(errors.CodeInvalidParam, "请求参数解析失败")
+	}
+
+	if err := h.service.UpdateStatus(c.UserContext(), uint(id), &req); err != nil {
+		return err
+	}
+
+	return response.Success(c, nil)
+}