workstation-v0 shortcut map contract

[mdheller]

Closes #126.

What changed:

• Added docs/workstation/shortcut-map.md.
• Added profiles/linux-dev/workstation-v0/bin/check-shortcut-map-contract.sh.
• Added workstation-shortcut-map smoke workflow.

Validation evidence:

• test -s docs/workstation/shortcut-map.md
• grep -F "Super+Shift+3" docs/workstation/shortcut-map.md
• bash -n profiles/linux-dev/workstation-v0/bin/check-shortcut-map-contract.sh
• bash profiles/linux-dev/workstation-v0/bin/check-shortcut-map-contract.sh

Known gaps:

• This is a contract/documentation validation PR only.
• It does not implement additional keybindings.

Non-goals preserved:

• No active keybinding changes.
• No remap daemon behavior changes.
• No package manifest changes.