[tests] Add SSH, networking, NTP, and home test suite.

[tests] Add SSH, networking, NTP, and home test suite.

- Replace placeholder key with generated keypair in tests/vps-base.scm
- Add tests/sshd.scm: service start, port 72, shell command via key auth
- Add tests/networking.scm: dhcpcd running
- Add tests/ntp.scm: ntpd running
- Add tests/claude-code.scm: installed and runnable
- Add tests/paseo.scm: installed
- Add tests/dotfiles.scm: .guile, .Xdefaults, gdbinit, nanorc
- Extend test OS with dak user and home packages
- Add TODO entry for blob storage SSH keys
- Fix guix-check hook to skip guild compile for test files
- Export %vps-operating-system from vps-system.scm

Co-Authored-By: Claude <noreply@anthropic.com>