chore(core): improve release workflow

[TylerVigario]

Summary

• Consolidates two-job (build + release) into a single job
• Auto-detects version bump from conventional commits, with optional manual override
• Gracefully skips when no version change is detected
• Uses RELEASE_NOTES.md (unreleased changes only) for GitHub Release body instead of full CHANGELOG.md
• Switches from npm run build to npm run build:dist (types already built during npm test)
• Adds build artifact verification step for debugging
• Release archive now includes both src/ (ESM source + types) and dist/ (ESM + UMD bundled)

Test plan

• Trigger with empty bump — verify auto-detection from commits
• Trigger with explicit patch — verify override works
• Trigger with no releasable commits — verify skip + warning
• Verify release archive contains src/ and dist/ directories
• Verify GitHub Release body uses unreleased notes only

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