feat: consolidate per-package changelogs into root CHANGELOG

[burczu]

Summary

• Adds scripts/consolidate-changelog.ts, run as part of ci:version, which aggregates the latest release entries from each packages/*/CHANGELOG.md into a single root CHANGELOG.md.
• Deduplicates entries across packages by PR number (falling back to commit hash, then raw text) and drops Updated dependencies noise.
• Idempotent: if the root CHANGELOG already contains the target version, the script is a no-op. New version blocks are spliced in above existing entries so the newest release stays on top.

The script is invoked automatically by the changesets/action release workflow, so the consolidated root CHANGELOG.md is committed and pushed as part of the auto-generated chore(release): version packages PR — no manual step required.

Test plan

• Trigger a dry run of yarn ci:version locally with pending changesets and verify root CHANGELOG.md is created/updated correctly.
• Verify idempotency by running yarn ci:version twice and confirming no duplicate version block is added.
• Confirm Updated dependencies lines are stripped and PRs are not duplicated across packages.
• Confirm the next chore(release): version packages PR opened by changesets/action includes the root CHANGELOG.md change.