feat(admin): 平台商户成员管理改用抽屉，消除商户视角切换与全局状态污染

- 交互重构：在「平台商户」与「平台账号」点击成员管理时，不再跳转路由或改写 localStorage.merchant_id，改为滑出 MerchantMembersDrawer 抽屉
- 抽屉能力：支持查看指定商户成员列表、新增成员（新建账号或关联已有账号）、修改角色与启用状态、移除成员
- 顶栏清理：彻底移除顶栏右上角的「当前商户：xxx」标签与「退出商户视角」按钮，超管登录自动清理任何残留上下文
- 后端补齐：新增平台专属 /api/platform/merchants/:id/members 与 roles 接口，平台操作不再依赖 X-Merchant-ID
- 验证：tsc -b && vite build 成功；全量 go test ./... 包含路由与鉴权回归测试 100% 通过

backend/internal/router/router.go

@@ -243,7 +243,11 @@ func Setup(h *Handlers) *gin.Engine {
 			platform.GET("/platform/orders", h.Merchant.ListPlatformOrders)
 			platform.POST("/platform/merchants", h.Merchant.CreateMerchant)
 			platform.PATCH("/platform/merchants/:id", h.Merchant.UpdateMerchantSettings)
+			platform.GET("/platform/merchants/:id/members", h.Merchant.ListPlatformMerchantMembers)
 			platform.POST("/platform/merchants/:id/members", h.Merchant.AddPlatformMerchantMember)
+			platform.PATCH("/platform/merchants/:id/members/:mid", h.Merchant.UpdatePlatformMerchantMember)
+			platform.DELETE("/platform/merchants/:id/members/:mid", h.Merchant.DeletePlatformMerchantMember)
+			platform.GET("/platform/merchants/:id/roles", h.Merchant.ListPlatformMerchantRoles)
 			platform.GET("/platform/product-catalog", h.Merchant.ListProductCatalog)
 			platform.GET("/platform/merchants/:id/products", h.Merchant.ListMerchantProductsByAdmin)
 			platform.PATCH("/platform/merchants/:id/products/:pid", h.Merchant.AdminUpdateMerchantProduct)

backend/internal/router/router_test.go

@@ -213,3 +213,30 @@ func TestRequestLoggerSuppressesPollingOnInfo(t *testing.T) {
 		t.Errorf("expected GET order to appear as [DEBUG] in DEBUG mode, got: %s", buf.String())
 	}
 }
+
+// TestPlatformMerchantMembersRoutes 验证平台管理员访问商户成员与角色接口完全独立于 X-Merchant-ID。
+func TestPlatformMerchantMembersRoutes(t *testing.T) {
+	engine, jm := newTestRouter(t)
+	token, err := jm.Generate(1, "admin", model.RoleAdmin)
+	if err != nil {
+		t.Fatalf("generate token: %v", err)
+	}
+
+	// 1. 获取商户 1 的成员列表
+	req := httptest.NewRequest("GET", "/api/platform/merchants/1/members", nil)
+	req.Header.Set("Authorization", "Bearer "+token)
+	w := httptest.NewRecorder()
+	engine.ServeHTTP(w, req)
+	if w.Code != 200 {
+		t.Fatalf("平台管理员查询商户成员应返回 200，实际 %d: %s", w.Code, w.Body.String())
+	}
+
+	// 2. 获取商户 1 的角色列表
+	req = httptest.NewRequest("GET", "/api/platform/merchants/1/roles", nil)
+	req.Header.Set("Authorization", "Bearer "+token)
+	w = httptest.NewRecorder()
+	engine.ServeHTTP(w, req)
+	if w.Code != 200 {
+		t.Fatalf("平台管理员查询商户角色应返回 200，实际 %d: %s", w.Code, w.Body.String())
+	}
+}