Centralize duplicated card shell, press animation, and color tokens

Extract the rounded-card shell and button press animation into a shared
CSS module composed by PageFrame, TitleScreen, and all buttons, add color
tokens for repeated values, and load the saved game once on mount.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/App.tsx

@@ -21,10 +21,8 @@ function clearGame() {
 }
 
 export default function App() {
-  const [page, setPage] = useState<Page>(() =>
-    loadGame() ? 'scoresheet' : 'title'
-  )
-  const [game, setGame] = useState<GameState | null>(() => loadGame())
+  const [game, setGame] = useState<GameState | null>(loadGame)
+  const [page, setPage] = useState<Page>(() => (game ? 'scoresheet' : 'title'))
 
   function handleNewGame() {
     clearGame()