feat: themed avatars and branding updates (#67)

## Summary

Added comprehensive avatar and branding updates across the library application:

### 🌸 Updated Main Branding
- New library-themed avatar (with playful "shh" gesture) for navigation icon
- Updated favicon and all PWA icons (10 sizes from 72x72 to 512x512)
- Added hero avatar to home page between title and subtitle
- All branding uses consistent circular styling with elegant hover effects

### 🎨 Media-Specific Avatars
Added unique themed avatars to each media list page:

- **🎮 Games**: Gaming setup with controller and LED lights (red #ff6b6b border)
- **📚 Books**: Reading in cozy library setting (brown #8b6f47 border)
- **🎵 Music**: Joyful with headphones and urban nightscape (blue #74b9ff border)
- **📺 Shows**: Relaxing with remote and theater curtains (pink #e84393 border)
- **📖 Manga**: Reading manga with shelves background (teal #00b894 border)
- **🎨 Art**: Art studio with paintbrush (yellow #fdcb6e border)

### ✨ Features
- 120x120px circular avatars with themed colour borders
- Smooth hover animations (scale + shadow effects)
- Centered hero sections at top of each list view
- Consistent styling across all media types
- Perfect integration with existing colour themes

### 📊 Technical Details
- All icons generated from source images at multiple resolutions
- Static assets served with correct MIME types
- Optimised image formats for performance
- Responsive design with proper accessibility attributes

## Test Plan

- [x] Verify navigation icon displays correctly in header
- [x] Check favicon appears in browser tabs
- [x] Test PWA icons on mobile devices
- [x] Confirm home page hero avatar renders properly
- [x] Verify all 6 media list avatars display with correct borders
- [x] Test hover animations on all avatars
- [x] Verify build succeeds
- [x] Check static assets serve with correct MIME types

🌸 Created with love by Hikari 💖

Reviewed-on: #67
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

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>