seo(site): add /troubleshooting/ page (connection-error queries) + internal links

Authentic troubleshooting content mapping the app's six connection-failure
diagnostics (malformed-url, no-internet, tls, health-failed, timeout,
server-unreachable) to concrete fixes. Targets real problem queries
('opencode mobile can't connect', 'opencode tailscale setup', 'network request
failed'). FAQPage + BreadcrumbList JSON-LD for rich results. Linked from landing,
guide, and download footers; added to sitemap.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs-site/sitemap.xml

@@ -15,6 +15,11 @@
     <changefreq>monthly</changefreq>
     <priority>0.8</priority>
   </url>
+  <url>
+    <loc>https://dzianisv.github.io/opencode-mobile/troubleshooting/</loc>
+    <changefreq>monthly</changefreq>
+    <priority>0.7</priority>
+  </url>
   <url>
     <loc>https://dzianisv.github.io/opencode-mobile/privacy/</loc>
     <changefreq>yearly</changefreq>