Epic: assembly-line work-order scene + 3D-space viewer

[bamdadd]

Assembly-line route: a multi-station work-order scene + a 3D-space viewer

Extend multicam-sim from "one object crosses a corridor" to a realistic manufacturing assembly line: 4-5 overlapping cameras watch an operator move along a line of workstations, performing the operations that assemble a product, and a work order (bill of materials) is ticked off operation-by-operation as each station is completed.

Domain-neutral and clean-room. It composes primitives that already exist — dsl/rig.py (CameraRig.stations/ring), dsl/motion.py (path DSL with .then()/.at_speed()), pose.py (COCO-17 skeleton), topology.py (Station/TransitEdge), order.py (BillOfMaterials/Order/verify_order/ActionEvent), and the runnable examples/assembly_station.py (already the operator+items+order-GT prototype).

Why

• A concrete, relatable scenario for the overlapping-camera + handoff + order-verification pipeline (today's MTMC scene is one abstract target). The single fixed assembly station already exists; this makes it a multi-station line with a moving operator.
• Analytic-first: perfect ground truth, deterministic, runs on a laptop in seconds. Pixels (Kubric photoreal) are optional polish; the geometry is the contract.
• A 3D-space viewer so the line's camera coverage/overlap is actually seeable, not just inferable from per-camera tiles.

Sub-issues

• Assembly-line scene builder: workstations + moving operator + overlapping camera rig #84 — Assembly-line scene builder (workstations + moving operator + overlapping camera rig)
• Assembly-line: station-completion -> work-order line-item events (order.json GT) #85 — Station-completion -> work-order line-item events
• 3D-space viewer: floor plan + camera frustums + stations + operator path (animated) #86 — 3D-space viewer (floor plan + camera frustums + stations + operator path)
• Docs: assembly-line walkthrough + README/vision update #87 — Docs: assembly-line walkthrough + README/vision update

Analytic-only for v1; Kubric photoreal is a follow-up, not a blocker.

[bamdadd]

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