Add service worker with Workbox: cache manifest, image cache, font cache, skip_waiting

- sw.js with network-first strategy, versioned cache, auto-purge old caches
- Workbox: cache_manifest, image_cache (30 days, 200 entries), font_cache (30 days, 10 entries)
- skip_waiting + clients.claim for instant updates
- CSP nonce for SW registration script
- Remove sw.js and workbox from .gitignore

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

public/sw.js

@@ -0,0 +1,47 @@
+const CACHE_VERSION = 'v1-' + Date.now()
+const CACHE_NAME = 'e-ticket-' + CACHE_VERSION
+
+const PRECACHE_URLS = [
+    '/',
+    '/evenements',
+    '/organisateurs',
+    '/favicon.png',
+    '/logo.png',
+]
+
+self.addEventListener('install', (event) => {
+    event.waitUntil(
+        caches.open(CACHE_NAME)
+            .then((cache) => cache.addAll(PRECACHE_URLS))
+            .then(() => self.skipWaiting())
+    )
+})
+
+self.addEventListener('activate', (event) => {
+    event.waitUntil(
+        caches.keys().then((cacheNames) =>
+            Promise.all(
+                cacheNames
+                    .filter((name) => name.startsWith('e-ticket-') && name !== CACHE_NAME)
+                    .map((name) => caches.delete(name))
+            )
+        ).then(() => self.clients.claim())
+    )
+})
+
+self.addEventListener('fetch', (event) => {
+    if (event.request.method !== 'GET') return
+
+    event.respondWith(
+        fetch(event.request)
+            .then((response) => {
+                if (response.ok) {
+                    const clone = response.clone()
+                    caches.open(CACHE_NAME).then((cache) => cache.put(event.request, clone))
+                }
+
+                return response
+            })
+            .catch(() => caches.match(event.request))
+    )
+})