Automate deployment scenario testing (Mithril/non-Mithril, Helm/Docker Compose)

## Why

We currently rely on manual testing for different deployment scenarios. As the stack grows (Helm, Docker Compose, health probes, multiple networks), we need automated verification that deployments work end-to-end across scenarios.

## What

Implement automated workflows to periodically test deployment scenarios:

- Full resync with Mithril snapshot (mainnet, preprod)
- Full resync without Mithril, from genesis (mainnet, preprod)
- Helm chart deployment (mainnet, preprod)
- Docker Compose deployment, clean state (mainnet, preprod)
- Validate sync completes and API responds correctly after deployment

Each run should record sync duration and store results for comparison across versions. This data helps detect performance regressions in sync time.

Initially proposed as a weekly workflow.

## Context

From 2026-04-02 Exchange tooling sync-up: team agreed on need for periodic automated deployment verification, especially ahead of the hard fork.