feat(mcp): add enabled count to panel info section

- Add enabledCount calculation using useMemo for performance
- Display format: "X MCP server(s) configured · Y enabled"
- Add i18n keys: mcp.enabledCount for zh and en
- Real-time updates when toggling server enabled status

src/i18n/locales/en.json

@@ -275,6 +275,7 @@
     "editCodexServer": "Edit Codex MCP",
     "configPath": "Config Path",
     "serverCount": "{{count}} MCP server(s) configured",
+    "enabledCount": "{{count}} enabled",
     "template": {
       "fetch": "Quick Template: mcp-fetch"
     },

src/i18n/locales/zh.json

@@ -275,6 +275,7 @@
     "editCodexServer": "编辑 Codex MCP",
     "configPath": "配置路径",
     "serverCount": "已配置 {{count}} 个 MCP 服务器",
+    "enabledCount": "已启用 {{count}} 个",
     "template": {
       "fetch": "快速模板：mcp-fetch"
     },