feat: allow custom base url

src/beaver_gateway/frontends/admin/templates/login.html

@@ -71,7 +71,7 @@
     {% if error %}
       <div class="error">{{ error }}</div>
     {% endif %}
-    <form method="post" action="/login">
+    <form method="post" action="{{ p }}/login">
       <label for="username">Username</label>
       <input id="username" name="username" type="text" autocomplete="username" required autofocus>
       <label for="password">Password</label>