fix(web): apply Terminal palette and UX fixes to game page

Aligns /play with the landing page and app color scheme — same
bg, panel, accent, and felt tokens from ui_theme.rs.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_server/web/game.html

@@ -28,7 +28,9 @@
     </header>
 
     <main>
-        <section id="board"></section>
+        <section id="board">
+            <div id="card-area"></div>
+        </section>
     </main>
 
     <div id="win-overlay" class="hidden">