feat: Phase 4 — responsive analysis pages + perf harness + god-component splits

Final phase of the UX modernization. Four conflict-free lanes.

Responsive (D4 — desktop+mobile 并重):
- 7 analysis pages made usable at 375px: grid-cols-4/5 → grid-cols-2 sm:*
  responsive variants; raw tables wrapped in overflow-x-auto; page overflow guards
- new e2e/responsive.spec.ts loops all 7 analysis routes at 375px asserting no
  horizontal scroll

Perf harness:
- playwright.config.ts gains an isolated `perf` project (testMatch /perf/), default
  chromium project excludes it (testIgnore)
- new e2e/perf.spec.ts: CDP Network.emulateNetworkConditions (Fast 3G) +
  PerformanceObserver LCP on /overview kpi-row + route-transition timing; numbers
  reported as a relative regression signal (dev-server, not a prod SLA), not gated

God-component splits (pure refactors, behavior-preserving):
- MonitoringDashboard 686 → 239 lines: extracted components/monitoring/* (StatsBar,
  OverviewTab, CaseStatsTab, DistrictStatsTab) + useMonitoringData hook; URL-granularity
  source-of-truth + drilldown reconcile kept in the orchestrator (no desync regression)
- AlertsDashboard 816 → 301 lines: extracted components/alerts/* (Toolbar, List,
  RiskPanel, MapPanel, DetailModal, …); role/privacy/grid-hide logic kept in the
  orchestrator — doctor-view privacy invariant (zero patient-point) still holds

Gates: tsc 0 · vitest 75 · functional e2e 37/37 (incl doctor-view privacy +
granularity + responsive) · build ok · perf project runs + reports

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/components/alerts/AlertsToolbar.tsx

@@ -0,0 +1,73 @@
+import React from 'react';
+
+interface AlertsToolbarProps {
+  forecastDay: 1 | 3 | 7;
+  onForecastDayChange: (day: 1 | 3 | 7) => void;
+  isFullscreen: boolean;
+  onToggleFullscreen: () => void;
+  onExportCsv: () => void;
+  onExportJson: () => void;
+}
+
+// Toolbar Row 1: 网格预测时效 + 全屏 + 导出.
+export const AlertsToolbar = React.memo(function AlertsToolbar({
+  forecastDay,
+  onForecastDayChange,
+  isFullscreen,
+  onToggleFullscreen,
+  onExportCsv,
+  onExportJson,
+}: AlertsToolbarProps) {
+  return (
+    <div className="card p-3 mb-3">
+      <div className="flex items-center gap-3 flex-wrap">
+        <div className="flex items-center gap-2">
+          <span className="text-[12px] text-text-muted">网格预测：</span>
+          <div className="flex gap-0.5 bg-bg-page p-0.5 rounded">
+            {([1, 3, 7] as const).map((day) => (
+              <button
+                key={day}
+                onClick={() => onForecastDayChange(day)}
+                className={`px-3 py-1 text-[12px] font-medium rounded transition-colors ${
+                  forecastDay === day
+                    ? 'bg-bg-card text-primary shadow-sm'
+                    : 'text-text-secondary hover:text-text-primary'
+                }`}
+              >
+                {day}天
+              </button>
+            ))}
+          </div>
+        </div>
+
+        <div className="w-px h-6 bg-border" />
+
+        <button
+          onClick={onToggleFullscreen}
+          className={`px-3 py-1.5 text-[12px] font-medium rounded transition-colors ${
+            isFullscreen
+              ? 'bg-bg-card text-primary border border-primary'
+              : 'bg-bg-page text-text-secondary border border-border'
+          }`}
+        >
+          {isFullscreen ? '退出全屏' : '全屏'}
+        </button>
+
+        <div className="w-px h-6 bg-border" />
+
+        <button
+          onClick={onExportCsv}
+          className="px-3 py-1.5 text-[12px] font-medium rounded bg-bg-page text-text-secondary border border-border hover:border-primary transition-colors"
+        >
+          导出CSV
+        </button>
+        <button
+          onClick={onExportJson}
+          className="px-3 py-1.5 text-[12px] font-medium rounded bg-bg-page text-text-secondary border border-border hover:border-primary transition-colors"
+        >
+          导出JSON
+        </button>
+      </div>
+    </div>
+  );
+});