docs: plan audio/video context support (#669)

* docs: plan audio/video context support

Closes #668

Signed-off-by: Nabin Mulepati <nmulepati@nvidia.com>

* docs: address audio video context plan feedback

Tighten the plan around legacy image-context migration, audio/video auto-detection, config-layer canonical blocks, capability gating, ImageColumnConfig scope, and single-PR implementation rollout.

Refs #668

* docs: clarify legacy image context migration

* docs: resolve image context canonical migration

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Signed-off-by: Nabin Mulepati <nmulepati@nvidia.com>

Author: nabinchha