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
Yard and zone soft-delete, refused with 409 while a yard still has
zones or a zone still holds inventory. warehouse_zones:delete was
missing from the catalog — the role presets spread every zone key, so
its absence crashes FreightPositionsSeeder at boot; a migration seeds
it everywhere.
Clicking a zone opens its contents as a datatable. Container identity
comes from booking_container_units for booked cargo and from
containers for backlog registrations; bulk cargo keeps its row with no
container number rather than disappearing from the zone.
