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>

static/js/scoreboard.js

@@ -1,6 +1,8 @@
 (function () {
     "use strict";
 
+    var BASE = document.body.dataset.baseUrl || "/";
+
     var loadingDiv = document.getElementById("scoreboard-loading");
     var recentSection = document.getElementById("recent-games-section");
     var recentTbody = document.querySelector("#recent-games-table tbody");
@@ -65,7 +67,7 @@
                 '  <div class="card-body">' +
                 '    <h5 class="card-title">' + escapeHtml(titleCase(c.name)) + '</h5>' +
                 '    <p class="card-text text-muted">' + c.completed_games + ' games completed</p>' +
-                '    <a href="/game" class="btn btn-accent btn-sm">Play</a>' +
+                '    <a href="' + BASE + 'game" class="btn btn-accent btn-sm">Play</a>' +
                 '  </div>' +
                 '</div>';
             popularRow.appendChild(col);
@@ -115,7 +117,7 @@
 
     async function loadScoreboard() {
         try {
-            var resp = await fetch("/api/scoreboard");
+            var resp = await fetch(BASE + "api/scoreboard");
             if (!resp.ok) throw new Error("Failed to load");
             var data = await resp.json();