feat: frps-manager v1.0 - frp 0.70.1 multi-tenant web management system

- Multi-tenant client/proxy management with Flask+SQLite
- Frps server control (start/restart/token rotation)
- Generate frpc.ini with shared server token + admin API
- Dashboard API integration (live client/proxy status)
- RBAC: admin/tenant_admin/user roles
- Audit logging for all operations
- Systemd service files included
- Requires legacy INI format (frp 0.70 TOML auth broken)

templates/error.html

@@ -0,0 +1,9 @@
+{% extends "base.html" %}
+{% block title %}{{ code }} · frps-manager{% endblock %}
+{% block content %}
+<div class="error-card">
+  <h1>{{ code }}</h1>
+  <p class="muted">{{ message }}</p>
+  <a class="btn" href="{{ url_for('dashboard') }}">回首页</a>
+</div>
+{% endblock %}