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

apps/web/vite.config.ts

@@ -17,4 +17,39 @@ export default defineConfig({
       },
     },
   },
+  build: {
+    target: "es2023",
+    cssTarget: "chrome120",
+    rollupOptions: {
+      output: {
+        manualChunks: {
+          "vendor-react": ["react", "react-dom", "react-router-dom"],
+          "vendor-antd": ["antd", "@ant-design/icons"],
+          "vendor-utils": ["axios", "zustand"],
+        },
+      },
+    },
+    minify: "terser",
+    terserOptions: {
+      compress: {
+        drop_console: true,
+        drop_debugger: true,
+        pure_funcs: ["console.log", "console.info", "console.debug"],
+      },
+    },
+    sourcemap: false,
+    reportCompressedSize: false,
+    chunkSizeWarningLimit: 600,
+  },
+  optimizeDeps: {
+    include: [
+      "react",
+      "react-dom",
+      "react-router-dom",
+      "antd",
+      "@ant-design/icons",
+      "axios",
+      "zustand",
+    ],
+  },
 });