pdpv0: make plan for how we'll integrate `pdpv0` with `main`

[BigLep]

Done Criteria

We have a documented and agreed upon plan between the "FS-WG" and Curio maintainers for how we'll reconcile pdpv0 with main. (Executing the plan will happen in other steps tracked in #822 ). The goal here is to get the client interactions working with the markets (v2) interface and wean our way off the pdpv0 flow and do away with those handlers.

Why Important

1. FOC/pdp is in a bad operational spot of not being on the branch that the Curio maintainers support.
2. We're splitting (diluting) resources between two branches rather combinging to make better singular product. The main markets v2 design gets us a number of improvements that the pdpv0 implementation cannot be enhanced to provide

[BigLep]

#fs-wg thread on this topic: https://filecoinproject.slack.com/archives/C08TVNKJV7C/p1764009188105729
Initial proposed plan: https://docs.google.com/document/d/1ICLkx80BkWGaxIqILB5VVg9e_JbztgRaHVmEwbUj_Ow/edit?tab=t.0