feat: set White/Black player names when exporting a PGN

Export PGN now opens a dialog with White/Black fields (pre-filled from the game
headers, placeholders treated as blank). Entered names are written back, so they
appear in the exported PGN, update the on-screen 'X vs Y' line, and persist if the
game is saved — instead of always exporting 'You vs Opponent'. Bump cache version.

src/chess_pressure/static/app.js

@@ -532,8 +532,26 @@
     updateSavedControls();
   }
 
-  function exportPGN() {
+  async function exportPGN() {
     if (!gameData) return;
+
+    // Let the user set player names before download; pre-fill from headers,
+    // treating placeholders ("?") as blank. Names are written back so they show
+    // on screen and persist on Save too.
+    const whiteEl = document.getElementById("pgn-white");
+    const blackEl = document.getElementById("pgn-black");
+    const real = (v) => (v && v !== "?" && v !== "????.??.??" ? v : "");
+    whiteEl.value = real(gameData.headers.White);
+    blackEl.value = real(gameData.headers.Black);
+    setTimeout(() => { whiteEl.focus(); whiteEl.select(); }, 0);
+
+    const ok = await openModal(document.getElementById("export-pgn-dialog"));
+    if (!ok) return;
+
+    gameData.headers.White = whiteEl.value.trim() || "White";
+    gameData.headers.Black = blackEl.value.trim() || "Black";
+    updateGameInfo();
+
     const pgn = ChessPressure.toPgn(gameData.headers, gameData.moves);
     const slug = (defaultGameName() || "game")
       .toLowerCase()

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=30">
+  <link rel="stylesheet" href="/style.css?v=31">
   <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>
@@ -135,6 +135,18 @@
     </form>
   </dialog>
 
+  <dialog id="export-pgn-dialog">
+    <form method="dialog">
+      <h2>Export PGN</h2>
+      <label>White: <input type="text" id="pgn-white" autocomplete="off" placeholder="White player"></label>
+      <label>Black: <input type="text" id="pgn-black" autocomplete="off" placeholder="Black player"></label>
+      <div class="dialog-buttons">
+        <button type="button" data-ok>Download</button>
+        <button type="button" data-cancel>Cancel</button>
+      </div>
+    </form>
+  </dialog>
+
   <dialog id="confirm-dialog">
     <form method="dialog">
       <h2 id="confirm-title">Please confirm</h2>
@@ -164,6 +176,6 @@
   <script src="/chess.min.js"></script>
   <script src="/gif.js"></script>
   <script src="/engine.js"></script>
-  <script src="/app.js?v=30"></script>
+  <script src="/app.js?v=31"></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-v30";
+const CACHE = "chess-pressure-v31";
 
 // Same-origin app shell. Cached by canonical path; the fetch handler matches
 // with ignoreSearch so cache-busting query strings (?v=NN) still hit.