fix(seo): add structured data for sitelinks and fix OG image

Replace Organization schema with WebSite schema, add SiteNavigationElement
for Documentation/FAQ/GitHub/Contact/Discord. Add BreadcrumbList to FAQ
and Contact pages. Remove outdated og-image.svg (source already uses PNG).
Update sitemap with lastmod and changefreq.

apps/landing/public/og-image.svg

@@ -1,12 +0,0 @@
-<svg xmlns="http://www.w3.org/2000/svg" width="1200" height="630" viewBox="0 0 1200 630">
-  <defs>
-    <linearGradient id="bg" x1="0%" y1="0%" x2="100%" y2="100%">
-      <stop offset="0%" style="stop-color:#f59e0b"/>
-      <stop offset="100%" style="stop-color:#ea580c"/>
-    </linearGradient>
-  </defs>
-  <rect width="1200" height="630" fill="url(#bg)"/>
-  <text x="600" y="280" text-anchor="middle" font-family="system-ui, -apple-system, sans-serif" font-size="72" font-weight="800" fill="white">SnapOtter</text>
-  <text x="600" y="350" text-anchor="middle" font-family="system-ui, -apple-system, sans-serif" font-size="28" font-weight="400" fill="rgba(255,255,255,0.85)">Self-Hosted Image Processing</text>
-  <text x="600" y="400" text-anchor="middle" font-family="system-ui, -apple-system, sans-serif" font-size="20" font-weight="400" fill="rgba(255,255,255,0.6)">50+ Tools · Local AI · 100% Offline · Open Source</text>
-</svg>

apps/landing/public/sitemap.xml

@@ -2,22 +2,32 @@
 <urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
   <url>
     <loc>https://snapotter.com/</loc>
+    <lastmod>2026-05-16</lastmod>
+    <changefreq>weekly</changefreq>
     <priority>1.0</priority>
   </url>
   <url>
     <loc>https://snapotter.com/faq</loc>
-    <priority>0.7</priority>
+    <lastmod>2026-05-16</lastmod>
+    <changefreq>monthly</changefreq>
+    <priority>0.8</priority>
   </url>
   <url>
     <loc>https://snapotter.com/contact</loc>
+    <lastmod>2026-05-16</lastmod>
+    <changefreq>monthly</changefreq>
     <priority>0.7</priority>
   </url>
   <url>
     <loc>https://snapotter.com/privacy</loc>
+    <lastmod>2026-05-16</lastmod>
+    <changefreq>yearly</changefreq>
     <priority>0.3</priority>
   </url>
   <url>
     <loc>https://snapotter.com/terms</loc>
+    <lastmod>2026-05-16</lastmod>
+    <changefreq>yearly</changefreq>
     <priority>0.3</priority>
   </url>
 </urlset>