Add delete-songs controls to admin request page

Operators can now select Version A and/or Version B in the Upload Songs
section and click 'Delete Selected Songs'. The handler removes the
chosen MP3 files, clears their DB paths, resets customer_approved to
'none', and sets the request status back to 'prompt_ready' so new
songs can be uploaded.

Bumps version to 0.5.1.

app.py

@@ -1126,6 +1126,42 @@ def admin_request(rid):
             )
             flash('Prompt saved.', 'success')
 
+        elif action == 'delete_songs':
+            # Remove selected uploaded MP3s and reset status so new songs can be uploaded.
+            to_delete = request.form.getlist('delete_song')
+            if not to_delete:
+                flash('Select at least one song to delete.', 'error')
+                return redirect(url_for('admin_request', rid=rid))
+
+            update_fields = {}
+            for version in to_delete:
+                if version == 'a':
+                    path = req.get('song_a_path')
+                    if path and Path(path).exists():
+                        try:
+                            Path(path).unlink()
+                        except OSError:
+                            pass
+                    update_fields['song_a_path'] = None
+                elif version == 'b':
+                    path = req.get('song_b_path')
+                    if path and Path(path).exists():
+                        try:
+                            Path(path).unlink()
+                        except OSError:
+                            pass
+                    update_fields['song_b_path'] = None
+
+            if update_fields:
+                # Wipe any prior customer approval because the old files are gone.
+                update_fields['customer_approved'] = 'none'
+                # Reset to prompt_ready since songs need to be uploaded again.
+                update_fields['status'] = 'prompt_ready'
+                update_request(rid, **update_fields)
+                flash('Selected songs deleted. Request reset to Prompt Ready.', 'success')
+            else:
+                flash('No uploaded songs selected for deletion.', 'error')
+
         elif action == 'upload_songs':
             # Save uploaded MP3 files for Version A and/or Version B.
             # Use the saved Suno title as the MP3 title tag if available.