feat: implement VPN platform management and real protocol services

frontend/src/style.css

@@ -0,0 +1,13 @@
+* { box-sizing: border-box; }
+html, body, #app { height: 100%; margin: 0; font-family: 'Helvetica Neue', Helvetica, 'PingFang SC', 'Microsoft YaHei', Arial, sans-serif; }
+body { background: #f5f7fa; }
+
+.stat-card { border-radius: 10px; padding: 20px; color: #fff; position: relative; overflow: hidden; }
+.stat-card .num { font-size: 32px; font-weight: 700; margin-top: 8px; }
+.stat-card .label { opacity: .85; font-size: 14px; }
+
+.page-card { border-radius: 10px; }
+
+.mono { font-family: 'JetBrains Mono', Consolas, monospace; font-size: 12px; white-space: pre-wrap; word-break: break-all; }
+
+.protocol-tag { font-weight: 600; }