Background process management for Pi. Start long-running commands without blocking the conversation.

ci: validate changesets before commit and publish master

A changeset landed with the bare package name instead of the scoped one, which changesets silently ignores at version time. scripts/check-changesets.ts checks every .changeset/*.md for a parseable frontmatter block, a package name matching package.json, a valid bump type, and a non-empty description. Wired into the pre-commit hook, the CI check job, and the publish job so a manual dispatch cannot skip it.