Hide the "In Development" banner once a game is open

The badge on the homepage and briefing page was static markup, wired
to nothing - flipping a game's status to open in the admin panel had
no effect on it. It's now driven by GameRepository::hasOpenGame() and
only shows while every game is still in development/locked.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

templates/website/home/intro.html.twig

@@ -81,7 +81,9 @@
             <div class="text-center mb-4">
                 <div class="dev-watermark-wrap">
                     <img src="{{ asset('images/AI_virus.png') }}" alt="AI Virus" class="img-fluid" style="max-height: 220px;">
-                    <span class="dev-watermark-badge">In Development</span>
+                    {% if showDevBanner %}
+                        <span class="dev-watermark-badge">In Development</span>
+                    {% endif %}
                 </div>
             </div>