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）

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

routes/admin_api/core.py

@@ -48,6 +48,36 @@ from services.time_utils import BEIJING_TZ, get_beijing_now
 logger = get_logger("app")
 config = get_config()
 
+_server_cpu_percent_lock = threading.Lock()
+_server_cpu_percent_last: float | None = None
+_server_cpu_percent_last_ts = 0.0
+
+
+def _get_server_cpu_percent() -> float:
+    import psutil
+
+    global _server_cpu_percent_last, _server_cpu_percent_last_ts
+
+    now = time.time()
+    with _server_cpu_percent_lock:
+        if _server_cpu_percent_last is not None and (now - _server_cpu_percent_last_ts) < 0.5:
+            return _server_cpu_percent_last
+
+        try:
+            if _server_cpu_percent_last is None:
+                cpu_percent = float(psutil.cpu_percent(interval=0.1))
+            else:
+                cpu_percent = float(psutil.cpu_percent(interval=None))
+        except Exception:
+            cpu_percent = float(_server_cpu_percent_last or 0.0)
+
+        if cpu_percent < 0:
+            cpu_percent = 0.0
+
+        _server_cpu_percent_last = cpu_percent
+        _server_cpu_percent_last_ts = now
+        return cpu_percent
+
 
 def _admin_reauth_required() -> bool:
     try:
@@ -738,7 +768,7 @@ def get_server_info_api():
     """获取服务器信息"""
     import psutil
 
-    cpu_percent = psutil.cpu_percent(interval=1)
+    cpu_percent = _get_server_cpu_percent()
 
     memory = psutil.virtual_memory()
     memory_total = f"{memory.total / (1024**3):.1f}GB"