feat(pwa): make the app installable

Manifest, gamepad icon (also the new favicon, instead of
the Vite logo), iOS meta tags and the tab title
ToBePlayed. No service worker, so a deploy never meets
an old cached bundle. The title bar color follows
light and dark mode. The README also lists adding a
game by name.

src/context/PreferencesContext.jsx

@@ -11,6 +11,8 @@ import {
 } from '../utils/appearance.js';
 
 const DARK_MODE_STORAGE_KEY = 'tbp_dark_mode';
+// The --background of style.css; the installed app paints its title bar in this color.
+const THEME_COLORS = {dark: '#09090b', light: '#fafafa'};
 
 const PreferencesContext = createContext(null);
 
@@ -28,6 +30,8 @@ export function PreferencesProvider({children}) {
         } else {
             document.documentElement.classList.remove('dark');
         }
+        document.querySelector('meta[name="theme-color"]')
+            ?.setAttribute('content', isDarkMode ? THEME_COLORS.dark : THEME_COLORS.light);
         localStorage.setItem(DARK_MODE_STORAGE_KEY, String(isDarkMode));
     }, [isDarkMode]);