feat: deep SEO optimization — metadata, OG tags, sitemap, structured data, GA4

- Add metadataBase and localized generateMetadata to all pages (EN/FR)
- Add Open Graph and Twitter card defaults with branded OG image
- Add canonical URLs and hreflang alternates on every page
- Create robots.ts (allow all, block /admin/ and /api/)
- Create sitemap.ts with all routes x 2 locales and hreflang
- Add Organization, WebSite, and CreativeWork JSON-LD structured data
- Add GA4 (G-LD348WF8EM) with Consent Mode v2 (default denied for EEA)
- Add llms.txt for AI discoverability
- Add production nginx config for letsbe.biz

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

nginx/letsbe.biz.conf

@@ -0,0 +1,60 @@
+# Redirect www → non-www
+server {
+    listen 80;
+    listen [::]:80;
+    server_name www.letsbe.biz;
+
+    # Certbot will upgrade this to https after cert is issued
+    return 301 http://letsbe.biz$request_uri;
+}
+
+# Main site
+server {
+    listen 80;
+    listen [::]:80;
+    server_name letsbe.biz;
+
+    # Certbot will add SSL config after:
+    #   sudo certbot --nginx -d letsbe.biz -d www.letsbe.biz
+
+    location / {
+        proxy_pass http://127.0.0.1:6974;
+        proxy_http_version 1.1;
+        proxy_set_header Upgrade $http_upgrade;
+        proxy_set_header Connection 'upgrade';
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_cache_bypass $http_upgrade;
+        proxy_read_timeout 86400;
+    }
+
+    # Static assets — long cache
+    location /_next/static/ {
+        proxy_pass http://127.0.0.1:6974;
+        proxy_cache_valid 200 365d;
+        add_header Cache-Control "public, max-age=31536000, immutable";
+    }
+
+    # Public assets
+    location /images/ {
+        proxy_pass http://127.0.0.1:6974;
+        proxy_cache_valid 200 30d;
+        add_header Cache-Control "public, max-age=2592000";
+    }
+
+    # Payload media uploads
+    location /media/ {
+        proxy_pass http://127.0.0.1:6974;
+        proxy_cache_valid 200 30d;
+        add_header Cache-Control "public, max-age=2592000";
+    }
+
+    # Security headers
+    add_header X-Frame-Options "SAMEORIGIN" always;
+    add_header X-Content-Type-Options "nosniff" always;
+    add_header Referrer-Policy "strict-origin-when-cross-origin" always;
+
+    client_max_body_size 50M;
+}