SEO overhaul: product schema, dynamic sitemap, favicon, og-image fix

- product.php: set metaTitle, metaDescription, canonicalUrl, ogImage,
  ogType=product, productSchema (JSON-LD with price/availability/reviews),
  and breadcrumbs variables for header.php to consume
- sitemap.php: dynamic XML sitemap generated from DB — includes all 30
  active products + static pages; robots.txt now points here
- header.php: fix favicon links (favicon.ico in root + icon-192.png);
  fix productSchema output (was double-encoding via json_encode)
- robots.txt: point Sitemap directive to /sitemap.php

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

sitemap.php

@@ -0,0 +1,42 @@
+<?php
+/**
+ * Tom's Java Jive - Dynamic XML Sitemap
+ */
+require_once __DIR__ . '/includes/functions.php';
+
+header('Content-Type: application/xml; charset=utf-8');
+header('X-Robots-Tag: noindex');
+
+$base = 'https://tomsjavajive.com';
+$now  = date('Y-m-d');
+
+$products = db()->fetchAll(
+    "SELECT product_id, updated_at FROM products WHERE is_active = 1 ORDER BY created_at DESC"
+);
+
+echo '<?xml version="1.0" encoding="UTF-8"?>' . "\n";
+echo '<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">' . "\n";
+
+// Static pages
+$staticPages = [
+    ['loc' => '/',            'priority' => '1.0', 'changefreq' => 'weekly'],
+    ['loc' => '/shop.php',    'priority' => '0.9', 'changefreq' => 'daily'],
+    ['loc' => '/about.php',   'priority' => '0.6', 'changefreq' => 'monthly'],
+    ['loc' => '/contact.php', 'priority' => '0.5', 'changefreq' => 'monthly'],
+    ['loc' => '/login.php',   'priority' => '0.3', 'changefreq' => 'monthly'],
+    ['loc' => '/register.php','priority' => '0.3', 'changefreq' => 'monthly'],
+];
+
+foreach ($staticPages as $p) {
+    $loc = htmlspecialchars($base . $p['loc']);
+    echo "  <url><loc>{$loc}</loc><lastmod>{$now}</lastmod><changefreq>{$p['changefreq']}</changefreq><priority>{$p['priority']}</priority></url>\n";
+}
+
+// Product pages
+foreach ($products as $product) {
+    $loc      = htmlspecialchars($base . '/product.php?id=' . $product['product_id']);
+    $lastmod  = substr($product['updated_at'] ?? $now, 0, 10);
+    echo "  <url><loc>{$loc}</loc><lastmod>{$lastmod}</lastmod><changefreq>weekly</changefreq><priority>0.8</priority></url>\n";
+}
+
+echo '</urlset>';