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/admin/admin.html

@@ -48,7 +48,8 @@
         </div>
     </div>
 
-    <!-- User Management Card -->
+    {% if current_user.is_admin %}
+    <!-- User Management Card (Admin Only) -->
     <div class="card management-card">
         <h2>👥 User Management</h2>
         <p>Manage application users, roles and permissions</p>
@@ -56,8 +57,17 @@
             <a href="{{ url_for('admin.user_management') }}" class="btn btn-primary">
                 Manage Users
             </a>
-            <a href="{{ url_for('admin.manage_editing_users') }}" class="btn btn-secondary" style="margin-left: 0.5rem;">
-                Manage Users That Edited Images
+        </div>
+    </div>
+    {% endif %}
+
+    <!-- Editing Users Card -->
+    <div class="card management-card">
+        <h2>✏️ Editing Users</h2>
+        <p>Manage user codes from players that edit images on-screen</p>
+        <div class="card-actions">
+            <a href="{{ url_for('admin.manage_editing_users') }}" class="btn btn-primary">
+                Manage Editing Users
             </a>
         </div>
     </div>
@@ -73,7 +83,8 @@
         </div>
     </div>
 
-    <!-- System Dependencies Card -->
+    {% if current_user.is_admin %}
+    <!-- System Dependencies Card (Admin Only) -->
     <div class="card management-card" style="background: linear-gradient(135deg, #f093fb 0%, #f5576c 100%);">
         <h2>🔧 System Dependencies</h2>
         <p>Check and install required software dependencies</p>
@@ -84,7 +95,7 @@
         </div>
     </div>
 
-    <!-- Logo Customization Card -->
+    <!-- Logo Customization Card (Admin Only) -->
     <div class="card management-card" style="background: linear-gradient(135deg, #fa709a 0%, #fee140 100%);">
         <h2>🎨 Logo Customization</h2>
         <p>Upload custom logos for header and login page</p>
@@ -94,6 +105,7 @@
             </a>
         </div>
     </div>
+    {% endif %}
 
     <!-- Quick Actions Card -->
     <div class="card">