Fix image download format - ensure PNG instead of WebP

- Return file path instead of PIL Image object
- Configure gr.Image with format='png' and type='filepath'
- Ensures steganography data is preserved in lossless PNG
- Prevents Gradio from converting to lossy WebP format

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app.py

@@ -75,9 +75,6 @@ def hide_data_in_image(image, secret_text, password, bits_per_channel):
                 os.unlink(output_path)
             return None, f"❌ **Error:** {message}"
 
-        # Load result image
-        result_img = Image.open(output_path)
-
         # Format success message
         result_message = f"""
 ✅ **Successfully Hidden!**
@@ -97,7 +94,9 @@ def hide_data_in_image(image, secret_text, password, bits_per_channel):
 - Keep your password safe if you used encryption
 """
 
-        return result_img, result_message
+        # Return the file path directly so Gradio serves the PNG file
+        # Don't delete output_path - Gradio needs it
+        return output_path, result_message
 
     except Exception as e:
         if 'input_path' in locals() and os.path.exists(input_path):
@@ -384,7 +383,7 @@ The image will look identical to the naked eye, but contains your secret message
                     hide_button = gr.Button("🔒 Hide Data in Image", variant="primary", size="lg")
 
                 with gr.Column(scale=1):
-                    hide_output_image = gr.Image(label="Result Image (Download This!)", height=300)
+                    hide_output_image = gr.Image(label="Result Image (Download This!)", height=300, format="png", type="filepath")
                     hide_output_text = gr.Markdown(label="Status")
 
             hide_button.click(