Allow overriding localStorage save key via ?game= query param

Defaults to 'incgame' when the query param is absent, preserving current behavior.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015ohELX137NFgWryS3BAY88

src/saveLoad.ts

@@ -5,15 +5,20 @@ export const saveParams = {
     path: 'default',
 }
 
-const KEY_GAME = 'incgame';
+const DEFAULT_KEY_GAME = 'incgame';
+
+function getKeyGame(): string {
+    const params = new URLSearchParams(window.location.search);
+    return params.get('game') || DEFAULT_KEY_GAME;
+}
 
 export function save(game: Game) {
-    localStorage.setItem(`${saveParams.path}_${KEY_GAME}`, serializeGameToString(game));
+    localStorage.setItem(`${saveParams.path}_${getKeyGame()}`, serializeGameToString(game));
 }
 
 export function load(): Game {
     try {
-        const raw = localStorage.getItem(`${saveParams.path}_${KEY_GAME}`);
+        const raw = localStorage.getItem(`${saveParams.path}_${getKeyGame()}`);
         if (raw)
             return deserializeGameFromString(raw);
     } catch (e) {