feat: add keyboard navigation, escape-to-close modals, skip-to-content (A11Y-02)

All modals now close with Escape key. Interactive card divs respond to
Enter key. Skip-to-content link added to Dashboard layout. All Web5 and
Settings modals get role=dialog, aria-modal, and escape handlers.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

neode-ui/src/views/Marketplace.vue

@@ -176,9 +176,11 @@
           data-controller-container
           :data-controller-install="!(isInstalled(app.id) || installingApps.has(app.id)) && (app.source === 'local' || !!app.dockerImage) ? '1' : undefined"
           tabindex="0"
+          role="link"
           class="glass-card card-stagger p-6 hover:bg-white/10 transition-all cursor-pointer flex flex-col"
           :style="{ '--stagger-index': index }"
           @click="viewAppDetails(app)"
+          @keydown.enter="viewAppDetails(app)"
       >
         <div class="flex items-start gap-4 mb-4">
         <img