User accounts now take priority over default filters within the user folders

Describe the bug
Since updating timeshift from 24.06.6 to 25.12.4, I noticed that default filters such as /home/*/.cache and /home/*/.local/share/[Tt]rash no longer take priority over any custom filters. This change appears to have been added in #342 to fix #341, however since the user account is kept in the same custom filter list this causes it to now take priority over the defaults, thus effectively removing any defaults within a user directory. In addition to that, attempting to manually add paths such as /home/*/.cache to the custom filter list results in them automatically being removed presumably because they are already in the default filter lists.

To Reproduce
Steps to reproduce the behaviour:

1. Make a new snapshot with a user's home folder included
2. Navigate to ~/.cache/ within the snapshot
3. Observe the folder's existence
4. Attempt to add /home/*/.cache to the filter list and watch it immediately vanish

Expected behaviour
The user's home directory should not automatically overwrite the defaults unless manually specified, and if a custom filter is already in the defaults it shouldn't be removed.

System:

• Linux Distribution Name and Version: Kubuntu 26.04 LTS
• Desktop: KDE
• Timeshift Version: 25.12.4
• Timeshift Mode [btrfs/rsync?]: rsync
• Display Server: wayland

Reproduce the issue in Timeshift using rsync with a user home folder included, then trace the filter handling described in issues #341 and #342. The fix is complete when default paths such as /home//.cache and /home//.local/share/[Tt]rash remain effective inside user folders, while explicitly duplicated custom filters are retained rather than removed.