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

@@ -347,7 +347,7 @@
     try {
       parsed = ChessPressure.parsePgn(g.pgn);
     } catch (e) {
-      alert("That saved game could not be loaded (corrupted PGN).");
+      modalAlert("That saved game could not be loaded (corrupted PGN).", "Couldn't load game");
       return;
     }
     applyParsed(parsed, savedId, true);
@@ -360,7 +360,7 @@
     try {
       parsed = ChessPressure.parsePgn(pgn);
     } catch (e) {
-      alert("Could not parse PGN — please check the format and try again.");
+      modalAlert("Could not parse PGN — please check the format and try again.", "Couldn't parse PGN");
       return;
     }
     applyParsed(parsed, null, isReference);
@@ -458,6 +458,28 @@
     });
   }
 
+  // Yes/no confirmation via the in-app dialog. Resolves true (OK) / false (cancel).
+  function modalConfirm(message, title) {
+    const dlg = document.getElementById("confirm-dialog");
+    document.getElementById("confirm-title").textContent = title || "Please confirm";
+    document.getElementById("confirm-msg").textContent = message;
+    dlg.querySelector("[data-cancel]").style.display = "";
+    return openModal(dlg);
+  }
+
+  // Single-button notice via the in-app dialog (replaces native alert()).
+  function modalAlert(message, title) {
+    const dlg = document.getElementById("confirm-dialog");
+    document.getElementById("confirm-title").textContent = title || "Notice";
+    document.getElementById("confirm-msg").textContent = message;
+    const cancel = dlg.querySelector("[data-cancel]");
+    cancel.style.display = "none";
+    return openModal(dlg).then((v) => {
+      cancel.style.display = "";
+      return v;
+    });
+  }
+
   async function saveCurrentGame() {
     if (!gameData) return;
     const dlg = document.getElementById("save-dialog");
@@ -502,8 +524,7 @@
     if (!currentSavedId) return;
     const g = getSavedGames().find((x) => x.id === currentSavedId);
     if (!g) return;
-    document.getElementById("confirm-msg").textContent = `Delete saved game "${g.name}"?`;
-    const ok = await openModal(document.getElementById("confirm-dialog"));
+    const ok = await modalConfirm(`Delete saved game "${g.name}"?`, "Delete game");
     if (!ok) return;
     setSavedGames(getSavedGames().filter((x) => x.id !== currentSavedId));
     currentSavedId = null;
@@ -511,8 +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=29">
+  <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>
@@ -135,9 +135,21 @@
     </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>Please confirm</h2>
+      <h2 id="confirm-title">Please confirm</h2>
       <p id="confirm-msg" class="export-info"></p>
       <div class="dialog-buttons">
         <button type="button" data-ok>OK</button>
@@ -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=29"></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-v29";
+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.