feat(warehouses): track physical container stack and slot positions

Extends the warehouse hierarchy below zone with ground stacks and vertical
slots, so a container's exact position is recorded rather than only its zone.

- freight.warehouse_zone_stacks / warehouse_zone_slots, plus nullable
  stack_id / slot_id on warehouse_inventory (existing rows stay valid)
- slot occupancy is derived from inventory status, guarded by a partial
  unique index, so no exit path has to remember to free a slot
- placement service: hierarchy validation, bottom-up stacking rules,
  accessibility/blocking-container reads, capacity vs slot summaries
- stack CRUD with auto-generated slots; reuses warehouse-zone permissions
- slot support folded into the existing move()/store() paths
- fix: validateLocation now rejects a mismatched warehouse/yard/zone triple
- seed:warehouse-layout builds the layout from a JSON config

apps/edr-freight-api/package.json

@@ -18,6 +18,7 @@
     "type-check": "tsc --noEmit",
     "seed:demo-scheduling": "ts-node -r tsconfig-paths/register src/scripts/seed-demo-scheduling.ts",
     "seed:freight-demo": "ts-node -r tsconfig-paths/register src/scripts/seed-freight-demo.ts",
+    "seed:warehouse-layout": "ts-node -r tsconfig-paths/register src/scripts/seed-warehouse-layout.ts",
     "seed:warehouse-demo": "ts-node -r tsconfig-paths/register src/scripts/seed-warehouse-demo.ts",
     "seed:warehouse-export-receive-ready": "ts-node -r tsconfig-paths/register src/scripts/seed-warehouse-export-receive-ready.ts",
     "seed:export-djibouti-interchange-demo": "ts-node -r tsconfig-paths/register src/scripts/seed-export-djibouti-interchange-demo.ts",