feat: 多主机纳管、用户认证、noVNC控制台、深色主题

主要功能:
- 多主机管理: 支持TCP/SSH方式纳管远程KVM主机
- 用户认证: JWT token认证, 默认admin/admin123
- noVNC控制台: 前端集成noVNC, WebSocket代理VNC连接
- 深色主题: 全局Element Plus深色主题覆盖
- 虚拟机操作: 克隆、迁移、XML编辑、快照管理
- 资源监控: CPU/内存/磁盘IO/网络流量实时监控

Bug修复:
- libvirt getInfo()内存单位修正(MiB非KiB)
- 远程主机VNC 0.0.0.0监听地址连接策略修复
- Dashboard定时器内存泄漏修复
- bcrypt版本兼容性修复

frontend/package-lock.json

@@ -9,6 +9,7 @@
       "version": "0.0.0",
       "dependencies": {
         "@element-plus/icons-vue": "^2.3.2",
+        "@novnc/novnc": "^1.7.0",
         "axios": "^1.15.2",
         "echarts": "^6.0.0",
         "element-plus": "^2.13.7",
@@ -193,6 +194,12 @@
         "@emnapi/runtime": "^1.7.1"
       }
     },
+    "node_modules/@novnc/novnc": {
+      "version": "1.7.0",
+      "resolved": "https://registry.npmjs.org/@novnc/novnc/-/novnc-1.7.0.tgz",
+      "integrity": "sha512-ucEJOx4T2avIRCleodk7YobZj5O2Ga2AeLfQ69A/yjG9HHba2+PDgwSkN3FttrmG+70ZGx21sElNFouK13RzyA==",
+      "license": "MPL-2.0"
+    },
     "node_modules/@oxc-project/types": {
       "version": "0.127.0",
       "resolved": "https://registry.npmjs.org/@oxc-project/types/-/types-0.127.0.tgz",