P0-12: Delete dead IIVision RGB camera class and unused exports #190

Part of #175 (audit Phase 0). Evidence: docs/audit/2026-11-09/detail/showcontrol-core.md §2.

Why. IIVision/camera.py:38-53 (RGBFrame) and :303-425 (OrbbecRGBCamera) existed only for the ArUco layout calibrator that ADR-0015 deleted. Zero importers outside IIVision. They need cv2 (camera.py:409-412), which no requirements file lists. Both are re-exported from IIVision/__init__.py:18,34-35.

Do.

• Delete RGBFrame, OrbbecRGBCamera, the cv2 import, and their section headers in camera.py; drop the exports from __init__.py.
• Drop unused imports: camera.py:19 (struct), :23 (contextmanager), :91 (OBAlignMode).
• Drop Blob3D.cam_half_extents_m, .median_z_m, .sample_count (blob_tracker.py:81-83, computed at :429-431, never read).
• Drop Calibration.delete() (blob_tracker.py:138-141; only mention is a docstring in pipeline.py:16).
• Drop CalibrationConfig (blob_tracker.py:47-49; only ever default-constructed at :158).
• Drop TrackState and PreStabilizeFilter from __init__.py exports (used only inside IIVision / redefined in flower_beds.py:353).

Done when. ~150 LOC gone; python -m pytest IIVision passes; pyflakes IIVision is clean.