feat: 新增配送合同附件安全上传功能

- 增加合同专用 PDF 上传、鉴权预览和失败清理接口
- 支持草稿附件替换移除、并发保护和启用完整性校验
- 修复循环模板引用导致文件选择器无法打开的问题
- 补充专项测试、中文项目文档和操作日志

backend/api/internal/routers/platform.go

@@ -70,8 +70,11 @@ func registerGasorderRoute(group *gin.RouterGroup) {
 	contract := group.Group("/gasorder_contract")
 	contract.GET("", gasorder.ListGasorderContract)
 	contract.POST("", gasorder.CreateGasorderContract)
+	contract.POST("/attachment/upload", gasorder.UploadGasorderContractAttachment)
+	contract.POST("/attachment/cleanup", gasorder.CleanupGasorderContractAttachment)
 	contract.GET("/:identity", gasorder.GetGasorderContract)
 	contract.PUT("/:identity", gasorder.UpdateGasorderContract)
+	contract.GET("/:identity/attachment", gasorder.ServeGasorderContractAttachment)
 	contract.POST("/:identity/activate", gasorder.ActivateGasorderContract)
 	contract.POST("/:identity/renew", gasorder.RenewGasorderContract)
 	contract.POST("/:identity/terminate", gasorder.TerminateGasorderContract)

backend/api/internal/routers/platform_contract_attachment_test.go

@@ -0,0 +1,27 @@
+// Package routers 测试平台合同附件专用路由注册。
+// 版本：v1.0.0
+package routers
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+)
+
+// TestPlatformRoutesExposeContractAttachmentEndpoints 验证专用接口独立于通用上传接口注册。
+func TestPlatformRoutesExposeContractAttachmentEndpoints(t *testing.T) {
+	engine := gin.New()
+	group := engine.Group("/heqi/platform/v1")
+	registerGasorderRoute(group)
+	routes := make(map[string]map[string]bool)
+	for _, route := range engine.Routes() {
+		if routes[route.Path] == nil {
+			routes[route.Path] = make(map[string]bool)
+		}
+		routes[route.Path][route.Method] = true
+	}
+	assertRouteMethods(t, routes, "/heqi/platform/v1/gasorder_contract/attachment/upload", http.MethodPost)
+	assertRouteMethods(t, routes, "/heqi/platform/v1/gasorder_contract/attachment/cleanup", http.MethodPost)
+	assertRouteMethods(t, routes, "/heqi/platform/v1/gasorder_contract/:identity/attachment", http.MethodGet)
+}