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>

tests/e2e/test_hello.py

@@ -0,0 +1,33 @@
+import pytest
+
+from app import make_app
+
+
+@pytest.fixture
+def app():
+    return make_app()
+
+
+async def test_homepage_returns_200(http_server_client):
+    response = await http_server_client.fetch("/")
+    assert response.code == 200
+
+
+async def test_game_returns_200(http_server_client):
+    response = await http_server_client.fetch("/game")
+    assert response.code == 200
+
+
+async def test_howtoplay_returns_200(http_server_client):
+    response = await http_server_client.fetch("/howtoplay")
+    assert response.code == 200
+
+
+async def test_about_returns_200(http_server_client):
+    response = await http_server_client.fetch("/about")
+    assert response.code == 200
+
+
+async def test_scoreboard_returns_200(http_server_client):
+    response = await http_server_client.fetch("/scoreboard")
+    assert response.code == 200