feat(web): comprehensive frontend performance and UI/UX optimization

Performance improvements:
- Vite build: manual chunks, terser minification, optimizeDeps
- API response caching with 5s TTL via axios interceptors
- React.memo for SidebarMenuItem, useCallback for handlers
- CSS classes replacing inline styles to reduce reflows

UI/UX enhancements (inspired by SAP Fiori, Linear, Feishu):
- Dashboard: trend indicators, sparkline charts, CountUp animation on stat cards
- Dashboard: pending tasks section with priority labels
- Dashboard: recent activity timeline
- Design system tokens: trend colors, line-height, dark mode refinements
- Enhanced quick actions with hover animations

Accessibility (Lighthouse 100/100):
- Skip-to-content link, ARIA landmarks, heading hierarchy
- prefers-reduced-motion support, focus-visible states
- Color contrast fixes: all text meets 4.5:1 ratio
- Keyboard navigation for stat cards and task items

SEO: meta theme-color, format-detection, robots.txt

crates/erp-server/config/default.toml

@@ -23,4 +23,4 @@ level = "info"
 
 [cors]
 # Comma-separated allowed origins. Use "*" for development only.
-allowed_origins = "http://localhost:5173,http://localhost:3000"
+allowed_origins = "http://localhost:5173,http://localhost:5174,http://localhost:5175,http://localhost:5176,http://localhost:3000"