feat(pwa): in-car PWA notifications use a full-screen ack dialog

Small sonner toasts are unreadable + untappable on a car dash.
Move SW registration into <SwNotifier/> so we have React state:
- Desktop / small-screen: normal sonner toasts (unchanged).
- In-car (detectInCar().isInCar): full-screen modal with 56px-tall
  buttons, big copy, finger-friendly Got it / Reload + Later actions.
- offline-ready dismisses on tap; needs-refresh has Later + Reload.

client/src/components/SwNotifier.tsx

@@ -0,0 +1,103 @@
+import { useEffect, useState } from 'react';
+import { toast } from 'sonner';
+import { registerSW } from 'virtual:pwa-register';
+import { detectInCar } from '../lib/incar';
+
+type Kind = 'offline-ready' | 'needs-refresh';
+
+export function SwNotifier() {
+  const [event, setEvent] = useState<Kind | null>(null);
+  const [updateSW, setUpdateSW] = useState<((reload?: boolean) => void) | null>(null);
+  const inCar = detectInCar().isInCar;
+
+  useEffect(() => {
+    if (!('serviceWorker' in navigator)) return;
+    const fn = registerSW({
+      immediate: true,
+      onNeedRefresh() { setEvent('needs-refresh'); },
+      onOfflineReady() { setEvent('offline-ready'); },
+    });
+    setUpdateSW(() => fn);
+  }, []);
+
+  // Desktop / small-screen UX: use a normal toast.
+  useEffect(() => {
+    if (!event || inCar) return;
+    if (event === 'offline-ready') {
+      toast.success('Ready to use offline', {
+        description: 'Your planned trip + map tiles will be available without signal.',
+      });
+      setEvent(null);
+    } else if (event === 'needs-refresh') {
+      toast('New version available', {
+        action: { label: 'Reload', onClick: () => updateSW?.(true) },
+        duration: Infinity,
+      });
+      setEvent(null);
+    }
+  }, [event, inCar, updateSW]);
+
+  if (!inCar || !event) return null;
+
+  // In-car: render a big full-screen acknowledgement with finger-friendly button.
+  const isUpdate = event === 'needs-refresh';
+  const dismiss = () => setEvent(null);
+  const action = () => {
+    if (isUpdate) updateSW?.(true);
+    else dismiss();
+  };
+
+  return (
+    <div
+      onClick={dismiss}
+      className="fixed inset-0 grid place-items-center p-8"
+      style={{ zIndex: 9999, background: 'rgba(5,5,8,0.82)' }}
+    >
+      <div
+        onClick={(e) => e.stopPropagation()}
+        className="w-full max-w-[560px] overflow-hidden"
+        style={{
+          background: 'var(--gd-bg-2)',
+          border: '1px solid var(--gd-border-2)',
+          borderRadius: 20,
+          boxShadow: '0 24px 60px rgba(0,0,0,0.55)',
+        }}
+      >
+        <div className="px-8 py-7" style={{ borderBottom: '1px solid var(--gd-border)' }}>
+          <div className="text-[12px] uppercase tracking-[0.2em] mb-3"
+               style={{ color: isUpdate ? 'var(--gd-amber)' : 'var(--gd-green)' }}>
+            {isUpdate ? 'New version available' : 'Ready to use offline'}
+          </div>
+          <div className="text-[22px] font-semibold leading-[1.25]">
+            {isUpdate
+              ? 'Reload to get the latest planner update'
+              : 'Your trip will be available without signal'}
+          </div>
+          <div className="text-[14px] mt-3" style={{ color: 'var(--gd-text-2)' }}>
+            {isUpdate
+              ? 'Your current plan stays the same. We just refresh the app.'
+              : 'Planned route, map tiles, and last-known itinerary are saved on this device. You can keep using the planner if LTE drops.'}
+          </div>
+        </div>
+        <div className="px-8 py-5 flex items-center gap-3" style={{ borderTop: '1px solid var(--gd-border)' }}>
+          {isUpdate && (
+            <button
+              onClick={dismiss}
+              className="flex-1 h-14 text-[16px] rounded-2xl"
+              style={{ background: 'var(--gd-panel-2)', border: '1px solid var(--gd-border)', color: 'var(--gd-text-2)' }}
+            >
+              Later
+            </button>
+          )}
+          <button
+            onClick={action}
+            className="flex-[2] h-14 text-[16px] rounded-2xl font-semibold"
+            style={{ background: 'var(--gd-red)', color: '#fff', boxShadow: '0 6px 24px rgba(227,25,55,0.35)' }}
+          >
+            {isUpdate ? 'Reload' : 'Got it'}
+          </button>
+        </div>
+      </div>
+    </div>
+  );
+}

client/src/main.tsx

@@ -1,38 +1,20 @@
 import React from 'react';
 import ReactDOM from 'react-dom/client';
 import { BrowserRouter } from 'react-router-dom';
-import { Toaster, toast } from 'sonner';
-import { registerSW } from 'virtual:pwa-register';
+import { Toaster } from 'sonner';
 import App from './App';
 import './styles/globals.css';
 import { detectInCar, applyInCarClass } from './lib/incar';
+import { SwNotifier } from './components/SwNotifier';
 
 applyInCarClass(detectInCar());
 
-// Register the service worker. autoUpdate strategy means a refresh picks up
-// the new build immediately — we still show a toast so the user knows.
-if (import.meta.env.PROD) {
-  const updateSW = registerSW({
-    immediate: true,
-    onNeedRefresh() {
-      toast('New version available', {
-        action: { label: 'Reload', onClick: () => updateSW(true) },
-        duration: Infinity,
-      });
-    },
-    onOfflineReady() {
-      toast.success('Ready to use offline', {
-        description: 'Your planned trip + map tiles will be available without signal.',
-      });
-    },
-  });
-}
-
 ReactDOM.createRoot(document.getElementById('root')!).render(
   <React.StrictMode>
     <BrowserRouter>
       <App />
       <Toaster position="top-center" richColors closeButton />
+      <SwNotifier />
     </BrowserRouter>
   </React.StrictMode>
 );