feat: battery-aware itinerary nudge + PWA / offline support

Battery nudge:
- lib/batteryPlan: project SoC through the planned stops using current
  Tesla battery (or 80% default), 85% of rated range, and conservative
  per-stop charge rates (Supercharger 1.5%/min, dest charger 0.4%/min).
- LegRow shows "arrive X%" plus a tone (red/amber/transparent) and a
  TIGHT / WON'T REACH chip if the projected arrival is below 15%/5%.
- Top-of-itinerary banner when any leg is danger or warning, naming the
  current SoC source (live Tesla vs assumed 80%).

PWA / offline:
- vite-plugin-pwa with autoUpdate strategy; ServiceWorker registered in
  main.tsx (prod-only).
- Workbox cache strategies:
    map tiles      CacheFirst, 30 days, 800 entries
    nominatim/OSRM NetworkFirst with cached fallback
    /api/*         NetworkFirst, short TTL, last response stays usable
- App shell precached so the planner renders offline; navigateFallback
  ensures deep links serve index.html without a network round trip.
- manifest.webmanifest + theme-color + favicon.svg (replaces dead
  /tesla-icon.svg reference). Installable to home screen.
- Sonner toasts on offline-ready and update-available.

client/vite.config.ts

@@ -1,9 +1,78 @@
 import { defineConfig } from 'vite';
 import react from '@vitejs/plugin-react';
 import { resolve } from 'path';
+import { VitePWA } from 'vite-plugin-pwa';
 
 export default defineConfig({
-  plugins: [react()],
+  plugins: [
+    react(),
+    VitePWA({
+      registerType: 'autoUpdate',
+      includeAssets: ['favicon.ico', 'apple-touch-icon.png'],
+      manifest: {
+        name: 'Grok Drive',
+        short_name: 'GrokDrive',
+        description: 'AI-assisted Tesla road trip planner',
+        theme_color: '#0a0a0c',
+        background_color: '#0a0a0c',
+        display: 'standalone',
+        orientation: 'any',
+        start_url: '/',
+        scope: '/',
+        icons: [
+          { src: '/favicon.svg', sizes: 'any', type: 'image/svg+xml' },
+        ],
+      },
+      workbox: {
+        globPatterns: ['**/*.{js,css,html,svg,ico,woff,woff2}'],
+        globIgnores: ['**/*.map'],
+        navigateFallback: '/index.html',
+        navigateFallbackDenylist: [/^\/api\//, /^\/\.well-known\//],
+        maximumFileSizeToCacheInBytes: 3 * 1024 * 1024,
+        runtimeCaching: [
+          // Map tiles — cache-first for offline viewing of the planned route.
+          {
+            urlPattern: ({ url }: { url: URL }) =>
+              url.hostname.endsWith('tile.openstreetmap.org')
+              || url.hostname.endsWith('basemaps.cartocdn.com')
+              || /tile/i.test(url.hostname),
+            handler: 'CacheFirst',
+            options: {
+              cacheName: 'map-tiles',
+              expiration: { maxEntries: 800, maxAgeSeconds: 60 * 60 * 24 * 30 },
+              cacheableResponse: { statuses: [0, 200] },
+            },
+          },
+          // Geocoding + routing APIs — network-first, with cached fallback.
+          {
+            urlPattern: ({ url }: { url: URL }) =>
+              url.hostname.endsWith('nominatim.openstreetmap.org')
+              || url.hostname.endsWith('router.project-osrm.org'),
+            handler: 'NetworkFirst',
+            options: {
+              cacheName: 'geo-api',
+              networkTimeoutSeconds: 4,
+              expiration: { maxEntries: 200, maxAgeSeconds: 60 * 60 * 24 * 7 },
+              cacheableResponse: { statuses: [0, 200] },
+            },
+          },
+          // Our own API — network-first, cached short-term so the last good
+          // response stays visible when LTE drops.
+          {
+            urlPattern: ({ url }: { url: URL }) => url.pathname.startsWith('/api/'),
+            handler: 'NetworkFirst',
+            options: {
+              cacheName: 'app-api',
+              networkTimeoutSeconds: 3,
+              expiration: { maxEntries: 50, maxAgeSeconds: 60 * 60 },
+              cacheableResponse: { statuses: [0, 200] },
+            },
+          },
+        ],
+      },
+      devOptions: { enabled: false },
+    }),
+  ],
   resolve: {
     alias: {
       '@': resolve(__dirname, './src'),