#file-box rendering glitches

[tremisabdoul]

#files-box becomes visible (with empty content) after switching from a
specific category back to 'All'. It seems like the widget gets allocated
in the layout but isn't properly hidden when empty.

Additionally, when searching, the #files-box border styling disappears
entirely, suggesting the widget may be getting destroyed and recreated
rather than simply shown/hidden. This might be related to why it appears
as a ghost element after the category switch (inconsistent widget
lifecycle management.)

Distro: Linux Sway Remix
nwg-drawer: v0.7.0

Steps to reproduce:

1. Add a border to #files-box in CSS
2. Open the drawer
3. Select a specific category
4. Go back to "All"
5. Scroll down > ghost #files-box appears
6. (Optional) Search for something > border disappears

Expected behavior:
#files-box should not be visible when empty