Prepare Screenstage v0.1.0 release

[jodonnell24]

Summary

• rename the package and config surface to Screenstage
• simplify the repo to one calm quickstart example and align starter scaffolding
• finish release metadata and add a committed sample capture to the README

Included

• package rename to screenstage
• screenstage.config.mjs starter and quickstart config naming
• cleaned example set down to a single quickstart
• sample output video + poster in the README
• updated changelog and release metadata

Verification

• npm run check
• npm run build
• npm run pack:check
• node dist/cli.js run ./examples/quickstart/screenstage.config.mjs