Selection mode in grid view

i've been facing some issue with file selection, i love how copyparty is keyboard focused, using with [vimium](https://addons.mozilla.org/en-US/firefox/addon/vimium-ff/) extension creates some problem for me.
first of all the using space to toggle doesn't work when files are in grid view.
it'd be great if you could add the file selection feature like dolphin have, either you could add a plus icon to select the file when in grid mode or right click drag to select the files as area selection

something like this

https://github.com/user-attachments/assets/edd57507-9663-40ad-92e4-0fedf45a7779

btw thank you for this awesome file server!!

also the icon of grid is deprecated i guess:

google chrome:

firefox:

version:
```
Dec 17 17:14:02 pchan copyparty[11398]: [SFX] this is: copyparty 1.19.23
Dec 17 17:14:02 pchan copyparty[11398]: [SFX] packed at: 2025-12-17, 00:17:27 UTC, 1765930647
Dec 17 17:14:02 pchan copyparty[11398]: [SFX] archive is: /usr/local/bin/copyparty-sfx.py
Dec 17 17:14:02 pchan copyparty[11398]: [SFX] python bin: /usr/bin/python3
Dec 17 17:14:02 pchan copyparty[11398]: [SFX] python ver: CPython 3.12.12 (main, Oct 11 2025, 15:09:54) [GCC 14.2.0]
Dec 17 17:14:02 pchan copyparty[11398]: [SFX] jinja2: bundled
Dec 17 17:14:02 pchan copyparty[11398]: [SFX] pyftpd: bundled
Dec 17 17:14:02 pchan copyparty[11398]: [SFX] sfxdir: /tmp/pe-copyparty.0.11398.0
```

The issue is about grid view selection in the web UI. Look at the frontend code handling file listings and grid view, likely in JavaScript/HTML. The user references a video showing area selection. Need to understand current selection logic and add new interaction modes (icon-based or drag selection). Check for existing UI components and event handlers. Testing will involve verifying selection works with keyboard shortcuts like space.

Written by the indexing model from the issue text.