feat: 发布管理全栈完善——环境值修复+驳回API+toast反馈+详情弹窗+确认框

后端:
- pipeline.go: 新增 RejectRelease handler(仅pending可驳回,状态置rejected)
- routes.go: 注册 POST /releases/:id/reject 路由

前端:
- ReleaseManager.tsx 重写(553→581行):
  - 修复环境值不匹配: development/production → dev/prod(与后端binding一致)
  - 移除硬编码mock applications数组,改自由输入应用名
  - 修复字段名: release.deployer → release.author
  - 新增toast反馈(create/approve/reject/deploy/rollback均有success/error)
  - 新增确认框(deploy/rollback操作前确认)
  - 新增发布详情弹窗(原缺失,Eye按钮无响应)
  - 新增空状态展示
  - 新增rejected状态徽章
  - 主题感知: bg-slate-800 → var(--dg-bg-secondary)
  - Select替换原生select下拉框
- api.ts: 新增 rejectRelease 方法

// Logan.Li

frontend/src/services/api.ts

@@ -251,6 +251,9 @@ export const releaseApi = {
   approveRelease: async (id: number | string) => {
     return http.post(`/releases/${id}/approve`);
   },
+  rejectRelease: async (id: number | string) => {
+    return http.post(`/releases/${id}/reject`);
+  },
   deployRelease: async (id: number | string) => {
     return http.post(`/releases/${id}/deploy`);
   },