Slate v2 Slate Browser Package Test Closure

Goal

Make the slate-browser package-local test command match the package proof claim instead of silently skipping the selection lane.

Completed

• updated packages/slate-browser/package.json so package-local test runs:
  • test:core
  • test:dom
  • test:selection
• updated packages/slate-browser/README.md to document the package-local test lane

Verification

• yarn workspace slate-browser test