fix: CPU显示修复 + 报表面板添加浏览器池状态

1. CPU 显示修复:
   - routes/admin_api/core.py: 新增 _get_server_cpu_percent()
   - 首次调用使用 interval=0.1 避免返回 0.0
   - 后续调用使用缓存，TTL 1秒

2. 报表面板浏览器池状态:
   - admin-frontend/src/api/browser_pool.js: 新增 API 调用
   - ReportPage.vue: 添加浏览器池状态卡片
   - 显示总/活跃/空闲 Worker 数和队列等待数
   - Worker 表格带状态颜色标签（活跃/空闲/异常）

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

static/admin/assets/email-JmyL2jV4.js

@@ -0,0 +1 @@
+import{a as n}from"./index-B9zsNTKQ.js";async function i(){const{data:a}=await n.get("/email/settings");return a}async function e(a){const{data:t}=await n.post("/email/settings",a);return t}async function c(){const{data:a}=await n.get("/email/stats");return a}async function o(a){const{data:t}=await n.get("/email/logs",{params:a});return t}async function l(a){const{data:t}=await n.post("/email/logs/cleanup",{days:a});return t}export{o as a,i as b,l as c,c as f,e as u};