Prevent overlapping partial assignments for the same deputy person

Stress Chrome testing used people with deputy roles on multiple lists. One run temporarily persisted the same deputy person on overlapping intervals and even displayed one candidate while submitting another role. A controlled fresh run confirmed adjacent non-overlapping intervals for Deputy 06 are valid and overlapping 01:00–04:00 reuse is correctly excluded initially; however other replacement-change selectors still offered people already serving partial intervals. Validate overlap by person across every initial/change/forwarding path, preserve valid adjacent intervals, and ensure submitted role identity always matches the displayed selection. Add multi-list deputy and boundary-time coverage.