Add PWA scanner app for organizers at /scanner

Standalone installable PWA with:
- JWT login via /api/auth/login
- Event list from /api/live/events
- QR code camera scanning (html5-qrcode library)
- Scan results with accepted/refused state and ticket details
- Auto token refresh on expiry
- Offline caching via service worker
- Dark theme optimized for outdoor scanning
- Vibration feedback on scan

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

public/scanner/sw.js

@@ -0,0 +1,27 @@
+const CACHE_NAME = 'scanner-v1';
+const ASSETS = [
+    '/scanner',
+    'https://unpkg.com/html5-qrcode@2.3.8/html5-qrcode.min.js',
+];
+
+self.addEventListener('install', (e) => {
+    e.waitUntil(caches.open(CACHE_NAME).then(c => c.addAll(ASSETS)));
+    self.skipWaiting();
+});
+
+self.addEventListener('activate', (e) => {
+    e.waitUntil(
+        caches.keys().then(keys => Promise.all(
+            keys.filter(k => k !== CACHE_NAME).map(k => caches.delete(k))
+        ))
+    );
+    self.clients.claim();
+});
+
+self.addEventListener('fetch', (e) => {
+    if (e.request.method !== 'GET') return;
+    if (e.request.url.includes('/api/')) return;
+    e.respondWith(
+        caches.match(e.request).then(cached => cached || fetch(e.request))
+    );
+});