add media upload functionality and management interface

templates/upload_content.html

@@ -21,6 +21,7 @@
     <div class="container py-5">
         <h1 class="text-center mb-4">Upload Content</h1>
         <form method="POST" enctype="multipart/form-data">
+            <input type="hidden" name="return_url" value="{{ return_url }}">
             <div class="mb-3">
                 <label for="target_type" class="form-label">Target Type:</label>
                 <select name="target_type" id="target_type" class="form-select" required {% if target_type %}disabled{% endif %}>