feat(warehouse,last-mile): truck load size rule, dedup last-mile, driver-required + arrival prefill

Truck loading:
- loadTruck enforces max 2 containers / one 40ft (two 20ft) and auto-marks an
  assigned truck arrived on load; container-items payload + modal expose
  container size with a client-side selection cap.
- Show "#x containers pending assignment" in the portal truck card and the
  backoffice container modal.

Last-mile:
- create() is idempotent — return the existing record for a booking instead of
  inserting a duplicate delivery row (fixed the same booking showing twice in
  Assign-Mile).
- setVehicles/update reject a truck with no assigned driver; the Assign toast
  now surfaces the reason.
- New GET /last-mile/booking/:id/arrival-trucks returns assigned EDR trucks with
  driver details; ReleaseOrderModal fetches and auto-fills them so an assigned
  EDR truck no longer reads as "not assigned yet".

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/edr-freight-web/backoffice/src/pages/operations/LastMilePage.tsx

@@ -666,8 +666,12 @@ const LastMilePage = () => {
       void qc.invalidateQueries({ queryKey: QUERY_KEYS.LAST_MILE.ROOT });
       void qc.invalidateQueries({ queryKey: ["vehicles"] });
     },
-    onError: () => {
-      toast({ title: "Assign failed", variant: "destructive" });
+    onError: (e: unknown) => {
+      // Surface the backend reason (e.g. "Truck … has no assigned driver …").
+      const raw = (e as { response?: { data?: { message?: string | string[] } } })?.response?.data
+        ?.message;
+      const description = Array.isArray(raw) ? raw.join(", ") : raw;
+      toast({ title: "Assign failed", description, variant: "destructive" });
     },
   });