chore: add release dry-run helper script

[dtsong]

Goal

Create a small script under scripts/ to run launch/release checks in one command (syntax checks, ops-check, installer smoke path, council-lite validator).

Why

A single dry-run command makes releases less error-prone and easier for contributors to repeat.

Acceptance Criteria

• Add a script (for example scripts/release-dry-run.sh)
• Script fails fast on first error and prints each phase name
• Cover checks listed in docs/release-checklist.md validation section
• Document usage in docs/release-checklist.md