fix: remove required attr from file input when existing video is selected

static/app.js

@@ -273,10 +273,8 @@
     form.addEventListener('submit', function () {
       if (videoPathInput.value) {
         form.action = '/upload/reuse';
-        fileInput.removeAttribute('required');
       } else {
         form.action = '/upload';
-        fileInput.setAttribute('required', '');
       }
       submitBtn.disabled = true;
       submitBtn.textContent = 'Starting...';
@@ -292,6 +290,11 @@
     submitHint.textContent = enabled
       ? 'Ready to start analysis.'
       : 'Select a video and at least one model to begin.';
+    if (selectedExistingVideo) {
+      fileInput.removeAttribute('required');
+    } else if (fileInput.files && fileInput.files.length === 0) {
+      fileInput.setAttribute('required', '');
+    }
   }
 
   /* ------------------------------------------------