Use XDG_CONFIG_HOME when creating welcome stubs in profile.d/toolbox.sh

**Describe the bug** `profile.d/toolbox.sh` is hardcoded to look for welcome stubs in `~/.config` which doesn't play nice if the user has set `XDG_CONFIG_HOME` to a different directory. **Steps how to reproduce the behaviour** 1. Set XDG_CONFIG_HOME to a non-default path (eg `~/.local/config`) 2. Create/enter a new toolbox 3. Find welcome stubs in `~/.config/toolbox` **Expected behaviour** Welcome files should be created relative to `$XDG_CONFIG_HOME/toolbox` **Actual behaviour** Welcome files were created in `~/.config/toolbox` **Screenshots** n/a **Output of `toolbox --version` (v0.0.90+)** `toolbox version 0.3` **Toolbx package info (`rpm -q toolbox`)** `toolbox-0.3-1.fc43.x86_64` **Output of `podman version`** ``` Client: Podman Engine Version: 5.7.1 API Version: 5.7.1 Go Version: go1.25.4 X:nodwarf5 Git Commit: f845d14e941889ba4c071f35233d09b29d363c75 Built: Tue Dec 9 18:00:00 2025 Build Origin: Fedora Project OS/Arch: linux/amd64 ``` **Podman package info (`rpm -q podman`)** `podman-5.7.1-1.fc43.x86_64` **Info about your OS** Fedora Silverblue 43 **Additional context** n/a