Make SuiviCPT an installable PWA

Adds what iOS/Android need to treat the site as an installable app
from Safari's "Add to Home Screen": a manifest.json, apple-touch-icon
set generated from the existing logo mark (scripts/generate-icons.mjs,
sharp as a dev dependency), and the apple-mobile-web-app-* meta tags
iOS Safari requires since it ignores manifest.json entirely.

The service worker is deliberately minimal — this app shows live
financial data, so navigations always hit the network first. It only
caches enough to serve offline.html when there's no connection, not a
full offline-first app shell.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

public/sw.js

@@ -0,0 +1,33 @@
+// Minimal service worker: exists only to satisfy PWA installability criteria
+// and give a usable offline fallback. Deliberately not a full offline-first
+// cache — this app shows live financial data, so navigations always go to
+// the network first; only the built Vite assets and the offline page are
+// cached, never HTML page content.
+const CACHE = 'suivicpt-shell-v1';
+const OFFLINE_URL = '/offline.html';
+
+self.addEventListener('install', (event) => {
+    event.waitUntil(
+        caches.open(CACHE).then((cache) => cache.add(OFFLINE_URL))
+    );
+    self.skipWaiting();
+});
+
+self.addEventListener('activate', (event) => {
+    event.waitUntil(
+        caches.keys().then((keys) =>
+            Promise.all(keys.filter((key) => key !== CACHE).map((key) => caches.delete(key)))
+        )
+    );
+    self.clients.claim();
+});
+
+self.addEventListener('fetch', (event) => {
+    if (event.request.mode !== 'navigate') {
+        return;
+    }
+
+    event.respondWith(
+        fetch(event.request).catch(() => caches.match(OFFLINE_URL))
+    );
+});