## Why
- Repository maintenance: standardize on Yarn 4 managed via Mise.
- Prepare for introducing minimum package-age constraints in dependency policy.
## How
- Migrated repo tooling to Yarn 4 with Mise.
- Updated CI and scripts for Yarn 4 behavior:
- Lerna invoked via `yarn run -T lerna`.
- Coverage args forwarded correctly (`-- --coverage`).
- Removed unsupported Yarn 4 `--silent` usage.
- Added missing package-local script dependencies surfaced by Yarn 4 (`jest`, `oxlint`, `rimraf`).
- Increased `EasCommand` coverage test timeout from 30s to 60s. (Was consistently failing in CI.)
## Test Plan
- CI only: `Run tests` matrix (including Node 20 coverage) and other touched workflows.
- Release behavior will be verified during the normal release run.
Stanisław Chmiela