fix: add active_page block to game template

Matches the active nav pattern from base.html updates.

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

templates/game.html

@@ -1,5 +1,7 @@
 {% extends "base.html" %}
 
+{% block active_page %}{% set active_page = "play" %}{% end %}
+
 {% block title %}Word Search — Play{% end %}
 
 {% block content %}