Add a CSV export for the Texas Hold'em hand history log

A dedicated dealer needs a paper trail that outlives the browser tab, not
just a scrollable in-app panel — the Export CSV button downloads the full
resolved-pot log (hand #, time, pot, payouts) for recordkeeping or a
disputed chip count after the session ends.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_015bnp7xKUPFFSpwkYNFaPgb

JoshHeaps.Net/Pages/Casino/TexasHoldem.cshtml

@@ -91,7 +91,10 @@
                 <div class="panelBody">
                     <div id="handHistoryList"></div>
                     <p id="handHistoryEmptyHint" class="fieldHint">Resolved pots show up here as you play, in case a chip count is disputed later.</p>
-                    <button id="clearHistoryBtn" class="holdemBtn holdemBtnSmall holdemBtnDanger">Clear history</button>
+                    <div class="handHistoryActions">
+                        <button id="exportHistoryBtn" class="holdemBtn holdemBtnSmall">Export CSV</button>
+                        <button id="clearHistoryBtn" class="holdemBtn holdemBtnSmall holdemBtnDanger">Clear history</button>
+                    </div>
                 </div>
             </details>
         </aside>
@@ -196,5 +199,6 @@
     <script src="~/js/casino/holdem/state.js?v=@ViewData["cssVersion"]"></script>
     <script src="~/js/casino/holdem/render.js?v=@ViewData["cssVersion"]"></script>
     <script src="~/js/casino/holdem/potWizard.js?v=@ViewData["cssVersion"]"></script>
+    <script src="~/js/casino/holdem/handHistoryExport.js?v=@ViewData["cssVersion"]"></script>
     <script src="~/js/casino/holdem/main.js?v=@ViewData["cssVersion"]"></script>
 }