feat(seo): add high-intent landing page(s) for organic acquisition (#129)

Add two new docs-site landing pages targeting search intent not covered
by existing pages:

- try-demo/ — "try an AI coding agent with no setup / no server", built
  around the real offline demo mode (scripted bug-fix walkthrough: login
  button + keyboard bug, reasoning, grep search, diff, permission prompt).
  Closes the gap between "curious about the app" and "willing to spin up
  a server" — zero existing pages address the no-setup demo path.
- gpt-gemini-android/ — "run GPT / ChatGPT / Gemini coding agent on
  Android", mirroring the existing claude-code-android page for the two
  other major providers opencode supports. Claude has its own page;
  GPT and Gemini did not.

Both pages match the existing docs-site template exactly (same CSS,
header/footer nav, OG/meta/JSON-LD pattern, favicon, canonical URL) and
are added to sitemap.xml. Ships live on the next `deploy-docs.sh` run.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

docs-site/sitemap.xml

@@ -61,6 +61,18 @@
     <priority>0.6</priority>
     <lastmod>2026-06-08</lastmod>
   </url>
+  <url>
+    <loc>https://dzianisv.github.io/opencode-mobile/try-demo/</loc>
+    <changefreq>monthly</changefreq>
+    <priority>0.8</priority>
+    <lastmod>2026-07-18</lastmod>
+  </url>
+  <url>
+    <loc>https://dzianisv.github.io/opencode-mobile/gpt-gemini-android/</loc>
+    <changefreq>monthly</changefreq>
+    <priority>0.8</priority>
+    <lastmod>2026-07-18</lastmod>
+  </url>
   <url>
     <loc>https://dzianisv.github.io/opencode-mobile/privacy/</loc>
     <changefreq>yearly</changefreq>