[Task]: Standardize on a Single Package Manager Across Project and CI

[jonulak]

🛠 Description
Unify the project and its GitHub Actions workflows to use one package manager (either npm or Yarn) instead of a mix of both. This will eliminate conflicting lockfiles, reduce build inconsistencies, and simplify dependency management.

✅ Acceptance Criteria
All local development scripts (install, build, test, etc.) invoke the chosen package manager exclusively.

Only one lockfile (package-lock.json or yarn.lock) remains in the repository; the other is removed.

All GitHub Actions workflows use the same package commands (npm ci / npm run … or yarn install / yarn …).

CI builds pass without errors after migration.

Documentation (README, CONTRIBUTING.md) is updated to reflect the chosen package manager and installation steps.

📋 Implementation Notes
Decide whether to standardize on npm or Yarn based on team preference and existing ecosystem compatibility.

Remove the unused lockfile and any configuration files (.npmrc, .yarnrc.yml) related to the abandoned manager.

Update scripts in package.json as needed to match the chosen tool’s CLI.

Modify each workflow file in .github/workflows/ to install dependencies and run scripts using the selected manager.

Run npm ci or yarn install --frozen-lockfile locally and in CI to verify consistency.