docs(mava): add scbe x sable integration review

[issdandavis]

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[issdandavis]

Closing this for now. This branch is a fork-local SCBE x Sable integration
review packet intended to guide evaluation inside my fork, not a ready
upstream change to Mava itself. I opened it against upstream prematurely. I
will keep exploratory notes and bridge work on my fork until there is a
concrete, generally useful change that belongs upstream. Thanks, and sorry
for the noise.