Initial commit: DHCP Web Manager

Flask-based web UI for managing ISC DHCP server (dhcpd).

Features:
- subnet / static host binding CRUD via web
- listen interface configuration (INTERFACESv4)
- active lease query + pool utilization stats
- service status, reload/restart, syntax check
- user auth + operation logs
- automatic backup before each config change
- safe change pipeline: write file → dhcpd -t → systemctl restart + is-active verify
- error messages include journalctl tail for diagnosis

templates/login.html

@@ -0,0 +1,14 @@
+{% extends "base.html" %}
+{% block title %}登录 · DHCP 管理{% endblock %}
+{% block content %}
+<div class="login-card">
+    <h1>📡 DHCP 管理</h1>
+    <p class="muted">请登录以管理 dhcpd 配置</p>
+    <form method="post" class="login-form">
+        <label>用户名 <input type="text" name="username" required autofocus></label>
+        <label>密码 <input type="password" name="password" required></label>
+        <button type="submit" class="btn btn-primary btn-block">登录</button>
+    </form>
+    <p class="muted small">默认账号：admin / admin（首次登录后请到"改密"修改）</p>
+</div>
+{% endblock %}