[epic] FBC channel schema with explicit semver support and simple edge mechanics

[grokspawn]

Current FBC schema express the full range of what olmv0 needs to express, but we can evolve schemas to create simpler and more powerful experiences for operator authors.

(There are separate concerns for v0 and v1, so this proposal is specifically constrained to v1.

1. write RFC (on its face, this looks not big enough for a brief)