Pass DIVE camera registrations to 2-cam/3-cam VIAME pipelines

[romleiaj]

Multicam pipelines previously received no transform information from DIVE; the old h5 workflow relied on paths hardcoded inside the pipes. Desktop and web now hand the dataset's camera registration to the pipeline's warp processes, mirroring the stereo calibration flow:

• One standard to_registration.json per non-reference camera is written into the job work dir; warpN (matching the pipeline camera position) receives its file via -s warpN:transformation_file=..., with the pair and direction pinned through the reader's from_camera/to_camera config since a pair may be stored in either orientation.
• Pipeline camera order is the registration reference first (the pipes warp everything onto camera 1's frame), then display order. Which detector a pipe runs on which input is the pipe's documented contract, not something DIVE infers.
• Only pairs registering a camera directly onto the reference are supported; pairs between two non-reference cameras are explicitly unsupported for pipelines and never reach the job. Cameras with points-only (unfitted) pairs get no settings.
• Web sends the registration as a multicam_registration job param built from dataset meta; the worker writes the files.

Requires VIAME's dive transform_2d_io reader and warp_detections process.

[romleiaj]

Paired with VIAME/VIAME#278.