Migrate CI and tooling to npm

[stesee]

No description provided.

[Copilot]

Pull request overview

This PR migrates the repository’s dependency locking, CI workflow, and supporting tooling from Yarn to npm, aligning local development, automation, and dependency update tooling around npm ci / package-lock.json.

Changes:

• Replace Yarn lockfile usage with package-lock.json and add an npm packageManager pin in package.json.
• Update documentation and CI workflow steps to use npm (npm install / npm ci, npm run build, Playwright install flow).
• Add Dependabot configuration for npm dependencies and GitHub Actions.

Reviewed changes

Copilot reviewed 4 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
yarn.lock	Removed Yarn lockfile as part of npm migration.
README.md	Updated install/build instructions to use npm and removed Yarn install snippet.
package.json	Added packageManager pin to document the intended npm version.
package-lock.json	Added npm lockfile (lockfileVersion 3) for reproducible installs via npm ci.
.github/workflows/release-branch.yml	Updated CI to use npm ci, added OS matrix build/test, and separated release creation with scoped permissions.
.github/dependabot.yml	Enabled weekly Dependabot updates for npm and GitHub Actions.

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