bitdynamics-ab/canton-devkit: docs/troubleshooting.md

# Troubleshooting Day-one setup (install, one working example, common breaks): [HackCanton Season 3 starter](hackcanton-s3.md). Failure modes and fixes. Start with `canton-devkit localnet doctor` — it runs the same host preflight as `localnet up` (Docker CLI, daemon, Compose v2, disk + memory headro