feat: BIND DNS Web Manager - Web interface for managing BIND9 DNS server

- Flask + SQLite web app with user authentication
- Zone management: create/delete zones, edit raw zone files
- Record management: add/delete A/AAAA/CNAME/MX/TXT/NS/PTR/SRV/CAA records
- Service control: start/stop/restart/reload BIND via systemctl/rndc
- Configuration editor: edit named.conf.options/local with syntax validation
- DNS query testing: online dig tool
- Audit log: all operations logged with user/timestamp
- BIND9 backend, listening on port 53

templates/error.html

@@ -0,0 +1,9 @@
+{% extends "base.html" %}
+{% block title %}错误 {{ code }}{% endblock %}
+{% block content %}
+<div class="error-page">
+    <div class="error-code">{{ code }}</div>
+    <div class="error-msg">{{ message }}</div>
+    <a href="{{ url_for('dashboard') }}" class="btn btn-primary">返回首页</a>
+</div>
+{% endblock %}