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/config.html

@@ -0,0 +1,63 @@
+{% extends "base.html" %}
+{% block title %}服务配置{% endblock %}
+{% block content %}
+<div class="page-head">
+    <h1>服务配置</h1>
+</div>
+
+<div class="card">
+    <h2>服务状态</h2>
+    <p>
+        状态：
+        {% if svc.active %}
+            <span class="badge badge-ok">● 运行中</span>
+        {% else %}
+            <span class="badge badge-warn">○ 未运行</span>
+        {% endif %}
+    </p>
+    {% if svc.status_text %}
+    <pre class="code-block small">{{ svc.status_text }}</pre>
+    {% endif %}
+    <form method="post" style="display:inline">
+        <input type="hidden" name="action" value="reload">
+        <button type="submit" class="btn">reload（不丢连接）</button>
+    </form>
+    <form method="post" style="display:inline"
+          onsubmit="return confirm('重启 dhcpd 会中断当前所有租约续约，确定？');">
+        <input type="hidden" name="action" value="restart">
+        <button type="submit" class="btn btn-warn">restart</button>
+    </form>
+</div>
+
+<div class="card">
+    <h2>语法检查</h2>
+    {% if syntax_ok %}
+        <p class="ok-text">✓ 配置语法 OK</p>
+    {% else %}
+        <p class="error-text">✗ 配置语法错误</p>
+    {% endif %}
+    {% if syntax_msg %}
+    <pre class="code-block small">{{ syntax_msg }}</pre>
+    {% endif %}
+</div>
+
+<div class="card">
+    <h2>监听接口</h2>
+    <p class="muted small">空格分隔多个接口，留空表示监听所有（生产环境强烈建议指定具体接口）</p>
+    <form method="post">
+        <input type="hidden" name="action" value="save_interfaces">
+        <label>INTERFACESv4
+            <input type="text" name="interfaces" value="{{ ifaces|join(' ') }}"
+                   placeholder="例如: enp0s31f6 或留空">
+        </label>
+        <div class="form-actions">
+            <button type="submit" class="btn btn-primary">保存（将重启 dhcpd）</button>
+        </div>
+    </form>
+</div>
+
+<div class="card">
+    <h2>当前 dhcpd.conf</h2>
+    <pre class="code-block">{{ conf }}</pre>
+</div>
+{% endblock %}