Implement editing users management and permission updates

- Added auto-creation of PlayerUser records from player metadata (user_card_data)
- Fixed player_user table schema (removed player_id, made user_code unique globally)
- Created admin page for managing editing users (view, update names, delete)
- Updated permissions: normal users can now access admin panel, editing users, and leftover media
- Admin-only access: user management, system dependencies, logo customization
- Fixed edited media workflow to preserve original files
- Content.filename now points to edited_media folder, keeping originals intact
- Added user display names in edited media page (shows name if set, code otherwise)
- Fixed leftover media file size calculation (handle None values)
- Split editing users into separate card on admin panel with description

app/templates/base.html

@@ -393,9 +393,7 @@
                         <img src="{{ url_for('static', filename='icons/playlist.svg') }}" alt="">
                         Playlists
                     </a>
-                    {% if current_user.is_admin %}
-                        <a href="{{ url_for('admin.admin_panel') }}">Admin</a>
-                    {% endif %}
+                    <a href="{{ url_for('admin.admin_panel') }}">Admin</a>
                     <a href="{{ url_for('auth.logout') }}">Logout ({{ current_user.username }})</a>
                     <button class="dark-mode-toggle" onclick="toggleDarkMode()" title="Toggle Dark Mode">
                         <img id="theme-icon" src="{{ url_for('static', filename='icons/moon.svg') }}" alt="Toggle theme">