fix: resolve Vue3Dropzone file wrapper access in SlideUploader

- Line 76: Add defensive guard to extract File from Vue3Dropzone wrapper {file: File, id: number}
- Line 79: Use actualFile.name for extension extraction (was file.name)
- Line 81: Use actualFile.name in error message (was file.name)
- Line 87: Append actualFile to FormData instead of wrapper (was file)

Vue3Dropzone v-model provides wrapped file objects, not raw File objects.
This fix ensures proper file access throughout the upload process.

resources/js/Components/SlideUploader.vue

@@ -73,17 +73,18 @@ function uploadNextFile(index) {
     }
 
     const file = files.value[index]
+    const actualFile = file.file || file  // Handle Vue3Dropzone wrapper {file: File, id: number}
 
     // Validate extension client-side
-    const ext = '.' + file.name.split('.').pop().toLowerCase()
+    const ext = '.' + actualFile.name.split('.').pop().toLowerCase()
     if (!acceptedExtensions.includes(ext)) {
-        uploadError.value = `"${file.name}" — Dateityp nicht erlaubt. Nur PNG, JPG, PPT, PPTX und ZIP.`
+        uploadError.value = `"${actualFile.name}" — Dateityp nicht erlaubt. Nur PNG, JPG, PPT, PPTX und ZIP.`
         uploading.value = false
         return
     }
 
     const formData = new FormData()
-    formData.append('file', file)
+    formData.append('file', actualFile)
     formData.append('type', props.type)
 
     if (props.serviceId) {