docs: update package README CI badge to main (#19692)

## Summary
Update the GitHub Actions CI status badge URLs in `packages/*/README.md`
to track `branch=main` instead of `branch=next`. This matches the root
README, keeps the badges consistent across the repo, and ensures the
displayed CI status reflects the default branch.

## Test plan
Docs-only change.
Verified the updated badge URLs in the modified `packages/*/README.md`
files use `ci.yml?branch=main`.