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/guide/index.html

@@ -235,7 +235,7 @@ footer a{margin:0 8px}
       <li id="step-server">
         <h3>Run <code>opencode serve</code> on your machine</h3>
         <p>Install OpenCode if you haven't already, then start it in server mode. Bind it to all interfaces and set a password so only you can connect:</p>
-        <pre><code>npm install -g opencode
+        <pre><code>npm install -g opencode-ai
 
 OPENCODE_SERVER_PASSWORD=yourpassword opencode serve --hostname 0.0.0.0 --port 4096</code></pre>
         <p class="muted">Configure your AI provider key on this machine (for example via OpenCode's auth flow or an environment variable). The key never leaves your server.</p>