feat(rates): last-mile rate rules with bulk per-ton-km and container distance bands

- rates: min_km/max_km columns, PER_TON_KM unit, ETB|USD currency for last mile
- extend UQ_rates_pattern with band start; overlap + shape validation
- shared last-mile charge resolver; approve-dialog price estimate endpoint
- delivery-fee invoice prices via rules, falls back to vehicle price/km
- backoffice: last-mile rate form (mode, container type, band, currency)

apps/edr-freight-api/src/contracts/contract-rate-schedule.builder.ts

@@ -43,6 +43,7 @@ const UNIT_LABELS: Record<string, string> = {
   PER_TON: 'per ton',
   PER_CONTAINER: 'per container',
   PER_KM: 'per km',
+  PER_TON_KM: 'per ton per km',
   PER_INVOICE: 'per invoice',
   FLAT: 'flat',
 };