feat(frontend): Phase 1 UX foundation — react-router v6 + responsive AppShell

Atomic foundation for the consensus-approved UX modernization (makes the
platform URL-addressable, refresh-safe, and mobile-usable for hospital demos).

- Migrate hand-rolled useState page switching → react-router v6 (routes.tsx,
  thin App.tsx auth gate, NavLink SideNav, lazy+Suspense per route)
- Add responsive AppShell: persistent rail (lg:) ⇄ off-canvas drawer + hamburger
  (<lg); kills hardcoded ml-[200px]; usable at 375px
- Add ui primitive kit (Skeleton/LoadingState/EmptyState/Card/Panel/Segmented)
- Sweep all raw "加载中..." text loaders → skeleton primitives (G4)
- Centralize test ids (utils/testids.ts); rewrite e2e for URL nav (17/17 pass:
  deep-link, refresh-preserves-page, back, 375px drawer/no-scroll)
- Harden DemographicAnalysis against API shape mismatch (defensive normalize)
- gitignore playwright-report/ and test-results/

Gates: tsc --noEmit 0 · pnpm build ok · e2e 17/17 · grep 加载中 zero outside ui/

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

frontend/src/components/CaseMap.tsx

@@ -1,4 +1,5 @@
 import { memo, useEffect, useRef, useState, useCallback } from 'react';
+import { Skeleton } from '@/components/ui';
 import L from 'leaflet';
 import 'leaflet/dist/leaflet.css';
 import { geocodedApi } from '@/services/api';
@@ -340,7 +341,7 @@ function CaseMapComponent({ height = '480px' }: CaseMapProps) {
           <div className="bg-bg-card/90 backdrop-blur rounded-lg border border-border-light shadow-sm px-3 py-2">
             <div className="text-[11px] text-text-secondary">
               {isLoading ? (
-                <span className="text-text-muted">数据加载中...</span>
+                <Skeleton className="h-3 w-20 inline-block align-middle" />
               ) : error ? (
                 <span className="text-danger">加载失败: {error}</span>
               ) : (