Deleting a phase now removes its assignments and actuals

For accounts with phase rescheduling enabled, DELETE /projects/{projectId}/phases/{phaseId} now deletes the phase's assignments and actuals instead of leaving them behind under No Phase, matching the behaviour in the app. Assignments and actuals on other phases are untouched, and the request is rejected if your API key's permissions don't allow deleting the related assignments or actuals. Accounts without phase rescheduling keep the previous behaviour.