GTK/desktop lane: add workstation mac-defaults validation check

[mdheller]

Parent tracker: #79

Summary

Add a dedicated validation check for the workstation-v0 mac-like GNOME defaults pack.

Why

The repository already carries a merged mac-like GNOME defaults script at:

• profiles/linux-dev/workstation-v0/gnome/mac-defaults.sh

That script is now part of the GTK/desktop substrate for the Mac-on-Linux lane, but there is not yet a dedicated repository check that makes the expected desktop behavior slice explicit.

Scope

Add a check that verifies the mac-defaults script still records the intended desktop behavior slice, including settings such as:

• hot corners disabled
• 12h clock
• locate pointer enabled
• Nautilus double-click policy
• dock favorites seed
• Files binding on Super+E
• Terminal binding on Super+Return

Acceptance criteria

• a dedicated validation check exists for the workstation mac-defaults script
• the check is wired into the repo validation surface
• workstation docs mention the validation hook explicitly
• follow-on PRs can reference this issue for GTK/desktop parity work

Proposed owner

@mdheller