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/src/Login.tsx

@@ -17,7 +17,7 @@ export default function Login({ onLogin }: { onLogin: () => void }) {
   return (
     <div className="center">
       <form className="login" onSubmit={submit}>
-        <img className="login-logo" src="/icons/logo.png" alt="" width={160} height={160} />
+        <img className="login-logo" src="/icons/logo.png" alt="" width={176} height={176} />
         <h1>Ham Lab</h1>
         <input type="password" autoFocus autoComplete="current-password" placeholder="password"
           value={pw} onChange={(e) => setPw(e.target.value)} disabled={busy} />