shared via /api/handoff-codes — edits affect every scope
Maps facility IDs to single-character (or short) codes shown on data-block Field E during handoffs.
The default section applies to all scopes; per-facility sections override for that scope's
perspective (e.g. PCT shows as E when viewed from ZDC, but as P by default).
Sector strings are appended automatically — e.g. PCT/2L renders as E2L on a ZDC scope.