Merge website-branding feature and adjust for compatibility

- Resolved conflicts in models.py, app.py, and template files
- Added branding checks to prevent errors when g.branding is None
- Updated all template references to use conditional branding
- Added BrandingSettings to migrations
- Created branding uploads directory
- Integrated branding with existing comment and task management features

templates/system_admin_dashboard.html

@@ -183,7 +183,10 @@
             <a href="{{ url_for('system_admin_settings') }}" class="btn btn-primary">
                 ⚙️ System Settings
             </a>
-            <a href="{{ url_for('system_admin_health') }}" class="btn btn-warning">
+            <a href="{{ url_for('system_admin_branding') }}" class="btn btn-primary">
+                🎨 Branding Settings
+            </a>
+            <a href="{{ url_for('system_admin_health') }}" class="btn btn-primary">
                 🏥 System Health
             </a>
         </div>