Fix web interface: show image upload for I2V mode

Users can now upload their own image for I2V mode instead of
only being able to generate one. The image upload box is now
visible in I2V mode, allowing users to either:
- Upload an existing image to animate
- Or let the system generate an image first

This provides more flexibility for the I2V workflow.

static/js/app.js

@@ -198,7 +198,8 @@ function switchMode(mode) {
         case 'i2v':
             i2vPrompts.classList.remove('hidden');
             imageModelGroup.classList.remove('hidden');
-            imageUploadBox.classList.add('hidden'); // Will generate image first
+            // Keep image upload visible - user can upload their own image OR generate one
+            imageUploadBox.classList.remove('hidden');
             break;
             
         case 't2i':
@@ -208,6 +209,7 @@ function switchMode(mode) {
             
         case 'i2i':
             strengthGroup.classList.remove('hidden');
+            // Image upload already visible by default
             break;
             
         case 'v2v':