Introduce company_secrets and company_secret_versions tables for
encrypted secret storage. Add EnvBinding discriminated union (plain vs
secret_ref) to replace raw string env values in adapter configs. Add
hiddenAt column to issues for soft-hiding. Improve migration system
with journal-ordered application and manual fallback when Drizzle
migrator can't reconcile history.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>