refactor(frontend): drop dead code in traffic and ws pipelines

Removes zero-consumer surface verified by repo-wide grep: the
reference-count render machinery, the never-called clearData chain,
unread snapshot fields (rangeMinutes, reason), dead refresh callbacks
on the connection hooks, the write-only wsRef sync, and the worker's
unreachable DEFAULT_CONFIG placeholder (now definite assignment under
the init-first client contract). No behavior change; the compressed
sampler path, samplerStats diagnostics, and lastTimestamp perf
contract stay. Net -120 lines across six files.

src/components/home/enhanced-traffic-stats.tsx

@@ -39,17 +39,6 @@ interface StatCardProps {
   onClick?: () => void
 }
 
-// 全局变量类型定义
-declare global {
-  interface Window {
-    animationFrameId?: number
-    lastTrafficData?: {
-      up: number
-      down: number
-    }
-  }
-}
-
 // 统计卡片组件 - 使用memo优化
 const CompactStatCard = memo(
   ({ icon, title, value, unit, color, onClick }: StatCardProps) => {