Add design spec for the contract-phase picker on the employee detail page.
Lets HR navigate past contract phases (e.g. 39h before a switch to FORFAIT,
or a closed CDD) so they can view and settle leftover CP/RTT balances
without changing the default behavior for the current contract.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
