feat: add About page with library information

Implements comprehensive About page (#51) with the following sections:
- Purpose: Explains that this is Naomi's curated collection
- Features: Overview of all 6 media types (Books, Games, Manga, Shows, Music, Art)
- How to Use: 5-step guide for browsing, liking, commenting, suggesting, and earning achievements
- Technology Stack: Details Angular, Fastify, MongoDB, Prisma, and other technologies
- Credits: Acknowledges Hikari as the developer and Naomi as the visionary
- Contact & Support: Links to Gitea, email, website, and Discord community
- Version Information: Current version and licence details

Technical implementation:
- New AboutComponent with responsive design
- Added /about route to app routes
- Added "ℹ️ About" link to user dropdown menu
- Beautiful purple gradient styling matching the witchy aesthetic
- FontAwesome icons for visual appeal
- Fully responsive for all device sizes

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

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

@@ -53,6 +53,7 @@ import { ApiService } from '../../services/api.service';
                   <a [routerLink]="['/profile', user.slug || user.id]" class="dropdown-item" (click)="closeDropdown()">My Profile</a>
                   <a routerLink="/settings" class="dropdown-item" (click)="closeDropdown()">Settings</a>
                   <a routerLink="/achievements" class="dropdown-item" (click)="closeDropdown()">🏆 Achievements</a>
+                  <a routerLink="/about" class="dropdown-item" (click)="closeDropdown()">ℹ️ About</a>
                   @if (!user.isAdmin) {
                     <a routerLink="/my-suggestions" class="dropdown-item" (click)="closeDropdown()">My Suggestions</a>
                   }