feat: implement initial user authentication, session management, and admin dashboard routing with

templates/setup.html

@@ -0,0 +1,18 @@
+{% extends "base.html" %}
+{% block title %}Setup Dungeon{% endblock %}
+{% block content %}
+<div class="card">
+    <h2>Initial Setup</h2>
+    <p style="color: var(--text-muted); margin-bottom: 1.5rem;">Create the initial admin user to access the dungeon.</p>
+    {% if let Some(err) = error %}
+    <div class="error">{{ err }}</div>
+    {% endif %}
+    <form method="POST" action="/__dungeon/setup">
+        <label>Username</label>
+        <input type="text" name="username" required autocomplete="off">
+        <label>Password</label>
+        <input type="password" name="password" required>
+        <button type="submit">Create Admin</button>
+    </form>
+</div>
+{% endblock %}