Assembly-line: station-completion -> work-order line-item events (order.json GT)

[bamdadd]

Part of #83. Depends on the assembly-line scene builder.

Tie the operator's route to a work order: as each workstation operation completes, tick off the matching line-item, so the run produces an order.json showing the assembly fulfilled step by step.

Scope

• Define the build as a BillOfMaterials / Order (the parts/operations that make one finished unit).
• Map station completion -> line-item: reaching + dwelling at a station emits a placement/action. Reuse order.ItemPlacement and order.ActionEvent (a place event time-synced to the frame, carrying the operator's hand-joint world position — the same channel examples/assembly_station.py uses).
  • e.g. station_1 -> base, station_2 -> subassembly, station_3 -> fasteners, station_4 -> inspection pass, station_5 -> unit complete (exact mapping is a design decision — propose in the PR).
• Run order.verify_order(...) and write the order.json sidecar; the analytic manifest stays byte-golden (order GT rides in the sidecar, per order.py).

Acceptance

• Deterministic order.json where status goes missing -> ... -> fulfilled as stations complete, one ActionEvent per station-completion at the correct frame.
• Test asserts final OrderStatus == fulfilled and action-event frames line up with the scene's dwell frames.
• Typed, mypy-strict, ruff clean.

Pointers

• src/multicam_sim/order.py (BillOfMaterials, Order, ItemPlacement, ActionEvent, verify_order, write_order_json), examples/assembly_station.py, issue Assembly-station: emit placement-synced operator action events (for causal action↔change fusion) #34 (placement-synced action events).

[bamdadd]

Closing: created by an automated process in error, not part of the roadmap.