New app icon and login logo: the HamLab penguin

Every icon is rendered from web/scripts/logo-source.png by scripts/icons.mjs: trimmed to
the artwork's own edge, transparent corners for the browser icons, a dark ground from the
artwork's palette for iOS (which paints transparency black) and for Android's maskable
icon, where the whole artwork sits inside the 80% safe circle. The login screen no longer
crops the logo to a circle or repeats the wordmark. Service worker cache bumped so
installed apps fetch the new files.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

web/public/sw.js

@@ -1,5 +1,5 @@
 // Ham Lab service worker: cache hashed assets, never the API, network-first for the shell.
-const CACHE = 'hamlab-v2';
+const CACHE = 'hamlab-v3'; // bumped when files under /icons/ change: they are served cache-first
 self.addEventListener('install', () => self.skipWaiting());
 self.addEventListener('activate', (e) => {
   e.waitUntil(caches.keys().then((ks) => Promise.all(ks.filter((k) => k !== CACHE).map((k) => caches.delete(k)))).then(() => self.clients.claim()));