feat: update branding with new library avatar

Updated all branding assets to use Naomi's library avatar (with the playful "shh" gesture):
- Navigation icon in header
- Favicon for browser tabs
- All PWA icon sizes (72x72 through 512x512, including maskable icons)
- Hero avatar on home page between title and subtitle

The avatar features consistent styling across all uses:
- Circular display with elegant borders
- Hover animations for interactive elements
- Shadows for visual depth
- Perfectly integrated with the witch-purple theme

All icons generated from the source image at multiple resolutions for optimal display on all devices and contexts.

apps/frontend/src/app/components/header/header.component.ts

@@ -18,7 +18,7 @@ import { ApiService } from '../../services/api.service';
     <header class="header">
       <nav class="navbar" aria-label="Main navigation">
         <div class="nav-brand">
-          <img src="/assets/icons/icon-72x72.png" alt="" class="brand-icon" role="presentation" />
+          <img src="/assets/nav-icon.jpg" alt="" class="brand-icon" role="presentation" />
           <h1><a routerLink="/">Naomi's Library</a></h1>
           @if (version()) {
             <span class="version" aria-label="Version {{ version() }}">v{{ version() }}</span>

apps/frontend/src/app/components/home/home.component.ts

@@ -23,6 +23,7 @@ import { Game, GameStatus, Book, BookStatus, Music, MusicType, Manga, MangaStatu
     <div class="container">
       <div class="hero">
         <h1>Welcome to Naomi's Library</h1>
+        <img src="/assets/nav-icon.jpg" alt="Naomi's avatar" class="hero-avatar" />
         <p class="tagline">A personal collection of games, books, music, manga, shows, and art</p>
       </div>
 
@@ -190,10 +191,28 @@ import { Game, GameStatus, Book, BookStatus, Music, MusicType, Manga, MangaStatu
 
     .hero h1 {
       font-size: 2.5rem;
-      margin-bottom: 0.5rem;
+      margin-bottom: 1rem;
       color: var(--witch-purple);
     }
 
+    .hero-avatar {
+      width: 150px;
+      height: 150px;
+      border-radius: 50%;
+      object-fit: cover;
+      border: 4px solid var(--witch-lavender);
+      box-shadow: 0 4px 12px var(--witch-shadow);
+      margin: 1rem auto;
+      display: block;
+      transition: all 0.3s;
+    }
+
+    .hero-avatar:hover {
+      transform: scale(1.05);
+      box-shadow: 0 8px 16px rgba(157, 78, 221, 0.5);
+      border-color: var(--witch-rose);
+    }
+
     .tagline {
       font-size: 1.2rem;
       color: var(--witch-plum);