Tighten TypeScript syntax checks

[andrewiggins]

What changed

This makes TypeScript stricter across the repository. It now catches unused labels, TypeScript syntax that needs runtime transformation, and imports that should only be used for types.

The settings live in one shared configuration used by every package and the kitchen sink example. Existing polyfill syntax that does not meet the new rules has narrow exceptions and TODOs so it can be cleaned up separately without weakening checks elsewhere.

Testing

• pnpm lint
• pnpm exec tsc --build --pretty --force
• pnpm build
• pnpm run test --coverage — 174 tests passed
• pnpm exec playwright test — 13 tests passed

[github-actions]

We detected some changes in public packages, and there are no updates in the .changeset directory.
If the changes are user-facing and should cause a version bump, run pnpm changeset to track your changes and include them in the next release CHANGELOG.
If you are making simple updates to repo configuration, examples, or documentation, you do not need to add a changeset.