Add comprehensive SEO optimization

Implement complete SEO setup for virtual product pages with:
- Meta tags (title, description, canonical, hreflang)
- Open Graph protocol for social sharing
- Twitter Card tags
- Schema.org structured data (JSON-LD) for products
- XML sitemap including virtual pages
- Dynamic meta tag updates via JavaScript

Changes:
- Create SEO snippet with all meta tags
- Add structured data snippet for products
- Generate sitemap.xml with products and hreflang
- Update meta tags dynamically when Shopify data loads
- Remove noindex/nofollow (was blocking all indexing)
- Add product-specific OG tags (price, availability)

All pages now properly indexed with correct multilingual setup.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

site/snippets/seo.php

@@ -0,0 +1,65 @@
+<?php
+/**
+ * SEO meta tags
+ */
+
+// Basic meta
+$title = $page->customTitle()->or($page->title())->value();
+$siteName = 'Index.ngo';
+$fullTitle = $title . ' | ' . $siteName;
+$description = $page->metaDescription()->or($page->description())->excerpt(160);
+$url = $page->url();
+$image = $page->image() ? $page->image()->url() : url('assets/og-image.jpg');
+
+// Language
+$lang = $kirby->language()->code();
+?>
+
+<!-- Basic Meta Tags -->
+<meta charset="UTF-8">
+<meta name="viewport" content="width=device-width, initial-scale=1.0">
+<title><?= $fullTitle ?></title>
+<?php if ($description): ?>
+<meta name="description" content="<?= $description ?>">
+<?php endif ?>
+
+<!-- Canonical & Alternate Languages -->
+<link rel="canonical" href="<?= $url ?>">
+<?php foreach($kirby->languages() as $language): ?>
+<link rel="alternate" hreflang="<?= $language->code() ?>" href="<?= $page->url($language->code()) ?>">
+<?php endforeach ?>
+<link rel="alternate" hreflang="x-default" href="<?= $page->url('fr') ?>">
+
+<!-- Open Graph -->
+<meta property="og:type" content="<?= $page->template() == 'product' ? 'product' : 'website' ?>">
+<meta property="og:site_name" content="<?= $siteName ?>">
+<meta property="og:title" content="<?= $title ?>" id="og-title">
+<meta property="og:description" content="<?= $description ?>" id="og-description">
+<meta property="og:url" content="<?= $url ?>">
+<meta property="og:image" content="<?= $image ?>" id="og-image">
+<meta property="og:image:width" content="1200">
+<meta property="og:image:height" content="630">
+<meta property="og:locale" content="<?= $lang == 'fr' ? 'fr_FR' : 'en_US' ?>">
+<?php foreach($kirby->languages() as $language): ?>
+<?php if ($language->code() != $lang): ?>
+<meta property="og:locale:alternate" content="<?= $language->code() == 'fr' ? 'fr_FR' : 'en_US' ?>">
+<?php endif ?>
+<?php endforeach ?>
+<?php if ($page->template() == 'product'): ?>
+<!-- Product-specific OG tags (will be updated by JS) -->
+<meta property="product:price:amount" content="0" id="og-price">
+<meta property="product:price:currency" content="EUR">
+<meta property="product:availability" content="in stock" id="og-availability">
+<meta property="product:brand" content="Index.ngo">
+<?php endif ?>
+
+<!-- Twitter Card -->
+<meta name="twitter:card" content="summary_large_image">
+<meta name="twitter:title" content="<?= $title ?>">
+<?php if ($description): ?>
+<meta name="twitter:description" content="<?= $description ?>">
+<?php endif ?>
+<meta name="twitter:image" content="<?= $image ?>">
+
+<!-- Favicon -->
+<link rel="icon" type="image/png" href="<?= url('assets/favicon.png') ?>">