Simplify release and Dependabot patch flow

[maelcaldas]

Summary

Simplify the release automation while keeping bkper-cli-delivery as the trusted npm publishing workflow.

Changes

• keep release publishing in bkper-cli-delivery
• simplify release label detection on main pushes by resolving the PR associated with the pushed commit
• remove the github-actions[bot] guard so label-driven releases work consistently
• collapse Dependabot Pi automation into one workflow that applies release:patch and enables auto-merge
• remove the separate Dependabot label workflow and drop the unused deps:pi label flow
• update maintainer release documentation in the README

Notes

• Dependabot Pi auto-merge now requires a non-GITHUB_TOKEN secret named BKPER_AUTOMERGE_TOKEN so the downstream main push can still trigger the trusted publisher release workflow.

Verification

• bun run build
• bun run test:unit