feat(backend): implement task creation and admin web

backend-api/internal/transport/webui/templates/partials.gohtml

@@ -0,0 +1,22 @@
+{{define "document-head"}}
+<meta charset="utf-8">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<meta name="color-scheme" content="light">
+<link rel="icon" href="data:,">
+<link rel="stylesheet" href="/static/admin.css">
+<script src="/static/admin.js" defer></script>
+{{end}}
+
+{{define "site-header"}}
+<a class="skip-link" href="#main-content">跳到主要内容</a>
+<header class="site-header">
+  <a class="brand" href="/tasks" aria-label="采购任务管理首页">
+    <span class="brand-mark" aria-hidden="true">采</span>
+    <span>采购任务管理</span>
+  </a>
+  <nav class="main-nav" aria-label="主导航">
+    <a href="/tasks" {{if .Page.TasksCurrent}}aria-current="page"{{end}}>任务列表</a>
+    <a href="/tasks/new" {{if .Page.NewCurrent}}aria-current="page"{{end}}>新建任务</a>
+  </nav>
+</header>
+{{end}}