fix(docs): correct server install command opencode -> opencode-ai (#113)

npm 'opencode' returns 404 (does not exist); the real package is
'opencode-ai' (v1.18.3, bin: opencode). Three docs-site pages — including the
setup guide the app's empty state and demo CTA link to — told users to run
'npm install -g opencode', which hard-fails at step 1 and bounces them before
they ever connect. Every other place in the repo already uses opencode-ai.
Verified via npm registry. Corrects guide/, landing index, and
opencode-on-phone pages.


Claude-Session: https://claude.ai/code/session_01T12AhSnQVrSxNnvwfCx2z6

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

docs-site/opencode-on-phone/index.html

@@ -228,7 +228,7 @@ footer a{margin:0 8px}
   opencode serve --hostname 0.0.0.0 --port 4096</code></pre>
       <p style="margin-bottom:0" class="muted">
         Setting a password turns on authentication so only you can connect. (Don't have opencode yet?
-        Install it with <code>npm install -g opencode</code>.)
+        Install it with <code>npm install -g opencode-ai</code>.)
       </p>
     </div>