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/views/SettingsView.vue

@@ -18,7 +18,7 @@
       <button
         @click="oauthSuccessProvider = null"
         aria-label="Dismiss notification"
-        class="text-gray-400 hover:text-gray-600 shrink-0"
+        class="text-gray-400 hover:text-gray-600 shrink-0 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-indigo-500 focus-visible:ring-offset-1 rounded"
       >
         <AppIcon name="x" class="w-4 h-4" />
       </button>
@@ -30,7 +30,7 @@
         v-for="tab in tabs"
         :key="tab.id"
         @click="activeTab = tab.id"
-        class="px-4 py-2 text-sm font-semibold border-b-2 transition-colors"
+        class="px-4 py-2 text-sm font-semibold border-b-2 transition-colors focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-indigo-500 focus-visible:ring-offset-1 rounded-t"
         :class="activeTab === tab.id
           ? 'text-indigo-600 border-indigo-600'
           : 'text-gray-500 hover:text-gray-700 border-transparent'"
@@ -64,7 +64,7 @@
         <button
           @click="oauthError = null"
           aria-label="Dismiss error"
-          class="text-red-400 hover:text-red-600 shrink-0"
+          class="text-red-400 hover:text-red-600 shrink-0 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-red-500 focus-visible:ring-offset-1 rounded"
         >
           <AppIcon name="x" class="w-4 h-4" />
         </button>