feat: add scoreboard with player names, per-category leaderboards, and themed tables

Add player_name column to games (migration included), with regex-based
validation and anti-abuse sanitization. New /scoreboard page shows recent
games from localStorage, popular categories with play counts, and top-10
per-category leaderboards sorted by completion time. Also includes
two-click reverse word matching, base URL prefix support for reverse-proxy
hosting, BasePageHandler refactoring, themed table CSS for all 5 themes,
and comprehensive test coverage for player names and scoreboard API.

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

handlers/__init__.py

@@ -0,0 +1,19 @@
+"""Shared handler base classes."""
+
+import tornado.web
+
+
+class BasePageHandler(tornado.web.RequestHandler):
+    """Base handler that injects ``base_url`` into all templates."""
+
+    def static_url(self, path, **kwargs):
+        url = super().static_url(path, **kwargs)
+        base_url = self.application.settings.get("base_url", "/")
+        if base_url != "/":
+            url = base_url + url.lstrip("/")
+        return url
+
+    def get_template_namespace(self):
+        ns = super().get_template_namespace()
+        ns["base_url"] = self.application.settings.get("base_url", "/")
+        return ns