mavweb: ui design system refresh — shared nav, cards, component classes

- Rewrote ui.css with design tokens, card/btn/badge/dot components
- All pages wrapped in <main class=page> with max-width container
- Replaced inline <style> blocks with ui.css classes
- passkey page now uses shared nav.site template
- PWA voice page unified under shared nav.site (no more separate tab nav)
- Inline lang toggle moved from nav to voice page body

cmd/mavweb/history.html

@@ -2,8 +2,8 @@
 <meta name=viewport content="width=device-width,initial-scale=1">
 <title>maven · history</title>
 <link rel=stylesheet href=/ui.css>
-<style>.val{word-break:break-all;max-width:20rem}</style>
 {{template "nav" "history"}}
+<main class=page>
 <h1>command history</h1>
 <p class=muted>{{len .Facts}} facts shown (newest first)</p>
 <div id=msg class=msg hidden></div>
@@ -16,9 +16,10 @@
 <td class=val>{{.Value}}</td>
 <td class=muted>{{.Source}}</td>
 <td>{{printf "%.2f" .Confidence}}</td>
-<td>{{if not .VoidsID}}<button onclick="revert('{{.Key}}',this)">revert</button>{{end}}</td>
+<td>{{if not .VoidsID}}<button class=btn onclick="revert('{{.Key}}',this)">revert</button>{{end}}</td>
 </tr>{{end}}
 </table></div>
+</main>
 <script>
 const msg=document.getElementById('msg');
 function revert(key,btn){