PDP and FWSS rollback procedure and script

## Context

Action item from the [2026-05-28 Hotfix FWSS v1.2.0 / PDPVerifier v3.4.0 postmortem](https://app.notion.com/p/filecoindev/2026-05-28-Hotfix-FWSS-v1-2-0-compatibility-with-PDPVerifier-v3-4-0-901dc41950c1820d99c88157214dec5d). During the hotfix incident, the team rolled forward rather than rolling back. We need a documented rollback procedure and supporting scripts so that rollback is a viable, low-friction option when an upgrade goes wrong.

Notion tracking: [PDP and FWSS have a rollback procedure and script](https://app.notion.com/p/filecoindev/PDP-and-FWSS-have-a-rollback-procedure-and-script-371dc41950c180689928c00651d4c040)

## Goals

- Document a clear rollback procedure for both PDP (PDPVerifier) and FWSS (FilecoinWarmStorageService) contract upgrades.
- Provide a script (or set of scripts) that can execute a rollback without requiring the operator to think through the steps under pressure.
- Cover both calibration and mainnet scenarios.
- Address when rollback is and isn't safe (e.g., state migrations that make rollback unsafe).

## Scope

This issue lives in filecoin-services but will require PRs in both repos:
- **FilOzone/filecoin-services** — FWSS rollback procedure and script
- **FilOzone/pdp** — PDPVerifier rollback procedure and script

## Related

- Release template improvements: #502