fix: 确保默认Admin账户存在且登录用户名不区分大小写

app/templates/admin/login.html

@@ -0,0 +1,11 @@
+{% extends 'base.html' %}
+{% block title %}后台登录{% endblock %}
+{% block content %}
+<h3 class="mb-3">管理员登录</h3>
+<form class="card p-3" method="post">
+  <input type="hidden" name="csrf_token" value="{{ csrf_token }}">
+  <div class="mb-3"><label class="form-label">用户名</label><input class="form-control" name="username" required></div>
+  <div class="mb-3"><label class="form-label">密码</label><input class="form-control" name="password" type="password" required></div>
+  <button class="btn btn-brand" type="submit">登录</button>
+</form>
+{% endblock %}