ci: reduce GitHub Actions runner usage

[yu-iskw]

Summary

Reduce repeated validation runner boundaries while preserving the distinct integration environment.

• consolidate package build, unit tests, and PR Trunk validation into one runner job
• keep integration tests as a separate downstream job
• remove redundant standalone Build and Trunk workflows
• skip docs/editor-only and draft PR runner allocation
• cancel superseded runs

Ready-for-review PRs keep the same validation commands with fewer repeated setup boundaries.