Folder overlap not detected when using tilde

[adiba]

Steps to reproduce

1. After setup, the default folder should be at /home/<username>/Sync. Click 'Add Folder' and enter ~/Sync or ~/Sync/a for the folder path.

Expected behavior

Following text should be shown:

Warning, this path is a subdirectory of an existing folder "Default Folder" (default).

Actual behavior

No warning is shown.

System information

Syncthing v1.27.3-rc.2 on Ubuntu 22

Further comments

I believe it would also be helpful to 1) require checking a box to confirm "I understand the implications" and 2) show the warning in the folder list as well.
Related issue would be detecting overlaps that are caused by symlinks.
As far as I can tell, overlap detection is currently happening on the frontend.