Fix check to only count bump files from current branch

[theoephraim]

Summary

• bumpy check was counting all pending bump files in .bumpy/, so it would pass even if the current branch didn't add one. Now it filters to only bump files added/modified on the branch, matching bumpy ci check behavior.
• Extracted shared filterBranchBumpFiles helper in bump-file.ts used by both check and ci check
• Fixed empty bump file handling in both commands — empty bump files (no releases) are now properly detected and pass the check

Test plan

• Push a branch with package changes but no bump file — bumpy check should fail
• Push a branch with package changes and a bump file — should pass
• Push a branch with an empty bump file — should pass with "no releases needed"
• Verify bumpy ci check still works correctly in CI

🤖 Generated with Claude Code

[bumpy-bot]

The changes in this PR will be included in the next version bump.

Patch releases

• @varlock/bumpy 1.0.0 → 1.0.1

Bump files in this PR

• fix-check-branch-filter.md (view diff) (edit)

Click here if you want to add another bump file to this PR

---

This comment is maintained by bumpy.