feat(11-05): visual consistency pass — typography, focus-visible, hover/active states, skeleton cleanup

- Normalize page titles to text-2xl font-semibold (was font-bold in TopicsView, DocumentView, SharedView)
- Normalize section titles to text-lg font-semibold (was text-xl in SettingsPreferencesTab, SettingsAiTab, SettingsCloudTab, BackupCodesDisplay, CloudCredentialModal)
- Normalize panel headings to text-sm font-semibold (SettingsAccountTab, DocumentView)
- Normalize AdminOverviewView page title from text-xl to text-2xl font-semibold
- Replace decorative sidebar skeleton inline styles with static Tailwind width classes (w-12/w-16/w-20)
- Add focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-indigo-500 focus-visible:ring-offset-1 to all interactive buttons across the app
- Add active:bg-* states to primary and secondary buttons for coherent press feedback
- Update nav-link scoped CSS in AppSidebar and AdminSidebar to include active:bg-gray-200 and focus-visible ring
- Add 7 new tests: VISUAL-01 skeleton class invariant, VISUAL-04 focus-visible invariant, VISUAL-03 typography invariant (36 test files, 270 tests pass)

frontend/src/components/auth/BackupCodesDisplay.vue

@@ -1,7 +1,7 @@
 <template>
   <div class="space-y-4">
     <div>
-      <h3 class="text-xl font-semibold text-gray-900 mb-1">Save your backup codes</h3>
+      <h3 class="text-lg font-semibold text-gray-900 mb-1">Save your backup codes</h3>
       <p class="text-sm text-gray-500">
         Store these codes somewhere safe. Each can only be used once if you lose access to your authenticator app.
       </p>
@@ -22,7 +22,7 @@
     <button
       type="button"
       @click="copyAll"
-      class="flex items-center gap-2 text-sm font-semibold text-indigo-600 hover:text-indigo-700 transition-colors"
+      class="flex items-center gap-2 text-sm font-semibold text-indigo-600 hover:text-indigo-700 transition-colors focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-indigo-500 focus-visible:ring-offset-1 rounded"
     >
       <!-- Clipboard icon -->
       <svg class="w-4 h-4" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" stroke-width="1.5" stroke="currentColor">
@@ -49,7 +49,7 @@
       type="button"
       @click="acknowledged && $emit('acknowledged')"
       :disabled="!acknowledged"
-      class="w-full px-6 py-3 bg-indigo-600 text-white rounded-lg text-sm font-semibold hover:bg-indigo-700 transition-colors min-h-[44px]"
+      class="w-full px-6 py-3 bg-indigo-600 text-white rounded-lg text-sm font-semibold hover:bg-indigo-700 active:bg-indigo-800 transition-colors min-h-[44px] focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-indigo-500 focus-visible:ring-offset-1"
       :class="!acknowledged ? 'opacity-50 cursor-not-allowed' : ''"
     >
       Enable two-factor authentication