chore: release 0.2.1

[mertushka]

Summary

Prepare the 0.2.1 patch release for the data-channel-first package.

This bumps package.json and package-lock.json from 0.2.0 to 0.2.1 after the native peer lifecycle fix and UDP mux Conformance test stabilization landed on main.

Verification

• npm run check
• npm run native:check
• npm run build - not run locally for version-only release prep; PR CI covers source build
• npm test
• npm run api:check
• npm run types:check
• npm run e2e:chrome - not run locally; PR CI covers when required by changed-file classification
• npm run wpt:selection:check - not run locally for version-only release prep
• npm run wpt:smoke - not run locally for version-only release prep
• npm run wpt:smoke:check - not run locally for version-only release prep
• npm run wpt:test / npm run wpt:check:strict - passed in manual Conformance on main commit 061f17c: https://github.com/mertushka/webrtc-node/actions/runs/28122928419

Also run locally: npm pack --dry-run --json, git diff --check.

WPT impact

No wpt-manifest.json, selected WPT result, or docs/divergences.md change. Manual Conformance passed before this version bump.

Browser interoperability

No browser behavior or coverage change in this release-prep PR.

Notes

Release workflow should be run from GitHub Release tag v0.2.1 after this PR is merged. publishConfig.access remains public; package publication remains on GitHub OIDC/provenance through the Release workflow.