docs: fix desktop browser list in iOS comparison table (#926)

The codebase only has CDP launchers for Chrome and Lightpanda
(cdp/chrome.rs, cdp/lightpanda.rs). Firefox and WebKit have no
launcher and are not supported.

Fixes part of #774

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

docs/src/app/ios/page.mdx

@@ -176,7 +176,7 @@ agent-browser -p ios --device "John's iPhone" open https://example.com
     <tr><th>Feature</th><th>Desktop</th><th>iOS</th></tr>
   </thead>
   <tbody>
-    <tr><td>Browser</td><td>Chromium/Firefox/WebKit</td><td>Safari only</td></tr>
+    <tr><td>Browser</td><td>Chrome, Lightpanda</td><td>Safari only</td></tr>
     <tr><td>Tabs</td><td>Supported</td><td>Single tab only</td></tr>
     <tr><td>PDF export</td><td>Supported</td><td>Not supported</td></tr>
     <tr><td>Screencast</td><td>Supported</td><td>Not supported</td></tr>