feat: add app icons and update UI with logo branding

src/app/features/about/about-panel.component.ts

@@ -56,8 +56,8 @@ import { trigger, transition, style, animate } from '@angular/animations';
         <div class="text-center space-y-6">
           <!-- Logo/Icon -->
           <div class="flex justify-center">
-            <div class="w-20 h-20 rounded-2xl bg-gradient-to-br from-nimbus-400 to-nimbus-600 flex items-center justify-center text-4xl shadow-lg">
-              📖
+            <div class="w-40 h-40 rounded-2xl bg-gradient-to-br from-nimbus-400 to-nimbus-600 flex items-center justify-center shadow-lg overflow-hidden">
+              <img src="assets/favicon.svg" alt="ObsiViewer" class="w-40 h-40" />
             </div>
           </div>
 

src/app/features/sidebar/app-sidebar-drawer.component.ts

@@ -19,7 +19,10 @@ import { TrashExplorerComponent } from '../../layout/sidebar/trash/trash-explore
            [class.translate-x-0]="mobileNav.sidebarOpen()">
       <!-- Header -->
       <div class="flex items-center justify-between p-4 border-b border-border dark:border-gray-800 bg-gradient-to-r from-nimbus-50 to-transparent dark:from-nimbus-900/20">
-        <h2 class="text-lg font-semibold truncate">{{ vaultName || 'ObsiViewer' }}</h2>
+        <div class="flex items-center gap-2 min-w-0">
+          <img src="assets/favicon.svg" alt="ObsiViewer" class="h-6 w-6 flex-shrink-0" />
+          <h2 class="text-lg font-semibold truncate">{{ vaultName || 'ObsiViewer' }}</h2>
+        </div>
         <button 
           (click)="mobileNav.toggleSidebar()" 
           class="p-2 rounded-full hover:bg-surface1 dark:hover:bg-card transition-all active:scale-95 transform flex-shrink-0">

src/app/features/sidebar/nimbus-sidebar.component.ts

@@ -17,7 +17,10 @@ import { VaultService } from '../../../services/vault.service';
     <div class="h-full flex flex-col overflow-hidden select-none">
       <!-- Header -->
       <div class="h-12 flex items-center justify-between px-3 border-b border-border dark:border-gray-800">
-        <div class="text-sm font-semibold truncate">{{ vaultName }} - ObsiViewer</div>
+        <div class="flex items-center gap-2 min-w-0">
+          <img src="assets/favicon.svg" alt="ObsiViewer" class="h-6 w-6 flex-shrink-0" />
+          <div class="text-sm font-semibold truncate">{{ vaultName }} - ObsiViewer</div>
+        </div>
         <button (click)="toggleSidebarRequest.emit()" class="p-2 rounded hover:bg-surface1 dark:hover:bg-card" title="Hide Sidebar">⟨⟨</button>
       </div>