fix(downloader): reset progress bar after completion (#4192)

# Description of Changes

- Added a `setTimeout` to hide the `.progressBarContainer` 1 second
after reaching 100%.
- Reset progress bar width to `0%` and `aria-valuenow` to `0` to prepare
for future downloads.
- This change ensures the UI does not leave a full progress bar
displayed after a completed download.


---

## Checklist

### General

- [x] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [x] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [x] I have performed a self-review of my own code
- [x] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

app/core/src/main/resources/static/js/downloader.js

@@ -482,6 +482,11 @@
     }
     progressBar.css('width', '100%');
     progressBar.attr('aria-valuenow', Array.from(files).length);
+    setTimeout(() => {
+      progressBar.closest('.progressBarContainer').hide();
+      progressBar.css('width', '0%');
+      progressBar.attr('aria-valuenow', 0);
+    }, 1000);
   }
 
   function updateProgressBar(progressBar, files) {