workstation-v0: extend aggregate polish helper with dock and shortcut signals

[mdheller]

Closed by PR #147.

Resolution:

• Extended check-workstation-polish.sh to aggregate shortcut map and GNOME dock/extension signals.
• Updated .github/workflows/workstation-polish-validation.yml to validate the expanded aggregate surface.
• Preserved the issue boundaries: no sourceos, doctor.sh, package manifest, GNOME defaults, keybinding, or extension mutation changes.

Validation evidence is recorded in PR #147.