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/notifications.html

@@ -2,8 +2,8 @@
 <meta name=viewport content="width=device-width,initial-scale=1">
 <title>maven · notifications</title>
 <link rel=stylesheet href=/ui.css>
-<style>.text{max-width:22rem}</style>
 {{template "nav" "notifications"}}
+<main class=page>
 <h1>notifications</h1>
 {{if .Nudges}}<div class=scroll><table>
 <tr><th>when</th><th>rule</th><th>channel</th><th>outcome</th><th>message</th></tr>
@@ -12,6 +12,7 @@
 <td class=key>{{.Rule}}</td>
 <td><span class=badge>{{.Channel}}</span></td>
 <td class={{.Outcome}}>{{.Outcome}}</td>
-<td class=text>{{.Message}}</td>
+<td class=text-max>{{.Message}}</td>
 </tr>{{end}}</table></div>
 {{else}}<div class=empty>no notifications yet</div>{{end}}
+</main>