Set up initial frontend with Vite and integrated Docker for full-stack build

frontend/public/favicon.svg

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+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32">
+  <rect width="32" height="32" rx="8" fill="#1a1814"/>
+  <text x="16" y="22" text-anchor="middle" font-family="serif" font-size="18" font-weight="700" fill="#e8b86d">B</text>
+</svg>

frontend/public/sw.js

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+const CACHE = 'budget-commun-v3'
+const ASSETS = ['/', '/index.html', '/manifest.json']
+
+self.addEventListener('install', e => {
+  e.waitUntil(caches.open(CACHE).then(c => c.addAll(ASSETS)))
+  self.skipWaiting()
+})
+
+self.addEventListener('activate', e => {
+  e.waitUntil(
+    caches.keys().then(keys =>
+      Promise.all(keys.filter(k => k !== CACHE).map(k => caches.delete(k)))
+    )
+  )
+  self.clients.claim()
+})
+
+self.addEventListener('fetch', e => {
+  // API : réseau uniquement, jamais de cache
+  if (e.request.url.includes('/api/')) return
+
+  // Assets statiques : network first → cache en fallback offline
+  e.respondWith(
+    fetch(e.request)
+      .then(response => {
+        const clone = response.clone()
+        caches.open(CACHE).then(c => c.put(e.request, clone))
+        return response
+      })
+      .catch(() => caches.match(e.request))
+  )
+})