fix: saving a game with an existing name overwrites instead of duplicating

saveCurrentGame always pushed a new entry, so re-saving under the same title
produced two dropdown entries. Now it warns + confirms, then replaces the
same-named game (case-insensitive), collapsing any existing duplicates into one.
Bump asset cache version.

src/chess_pressure/static/app.js

@@ -422,7 +422,17 @@
     const name = (prompt("Save game as:", defaultGameName()) || "").trim();
     if (!name) return;
     const pgn = ChessPressure.toPgn(gameData.headers, gameData.moves);
-    const saved = getSavedGames();
+    let saved = getSavedGames();
+
+    // Overwrite an existing game with the same name (case-insensitive) instead of
+    // creating a duplicate; also collapses any pre-existing duplicates.
+    const key = name.toLowerCase();
+    const exists = saved.some((g) => g.name.toLowerCase() === key);
+    if (exists) {
+      if (!confirm(`A game named "${name}" already exists. Overwrite it?`)) return;
+      saved = saved.filter((g) => g.name.toLowerCase() !== key);
+    }
+
     const id = "g" + Date.now().toString(36);
     saved.push({ id, name, pgn, savedAt: new Date().toISOString() });
     setSavedGames(saved);

src/chess_pressure/static/index.html

@@ -4,7 +4,7 @@
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>Chess Pressure</title>
-  <link rel="stylesheet" href="/style.css?v=26">
+  <link rel="stylesheet" href="/style.css?v=27">
   <link rel="stylesheet" href="https://unpkg.com/@chrisoakman/chessboardjs@1.0.0/dist/chessboard-1.0.0.min.css">
   <link rel="manifest" href="/manifest.json">
 </head>
@@ -139,6 +139,6 @@
   <script src="/chess.min.js"></script>
   <script src="/gif.js"></script>
   <script src="/engine.js"></script>
-  <script src="/app.js?v=26"></script>
+  <script src="/app.js?v=27"></script>
 </body>
 </html>

src/chess_pressure/static/sw.js

@@ -7,7 +7,7 @@
  *
  * Bump CACHE on every deploy so clients pick up new assets.
  */
-const CACHE = "chess-pressure-v26";
+const CACHE = "chess-pressure-v27";
 
 // Same-origin app shell. Cached by canonical path; the fetch handler matches
 // with ignoreSearch so cache-busting query strings (?v=NN) still hit.