test: validate TypeScript checkpoint continuation example

[rlippmann]

Summary

Adds the existing TypeScript checkpoint-continuation example package to the repository’s standard TypeScript validation scripts.

The package was already present and functional but was not included in the normal validation path.

Why

The checkpoint-continuation example had tests, typechecking, and build support, but the repository validation scripts did not execute it.

Including the package in normal validation improves coverage and helps ensure checkpoint-continuation behavior remains validated alongside the rest of the TypeScript examples.

Changes

• Added typescript/examples/checkpoint_continuation to:
  • scripts/validate_typescript_fast.sh
  • scripts/validate_typescript.sh
• Added the package to the existing build-eligible path used by the validation scripts.

Validation

• ./scripts/validate_typescript_fast.sh passed
• ./scripts/validate_typescript.sh passed
• The checkpoint-continuation package successfully ran:
  • npm test
  • npm run typecheck
  • npm run build

Scope

This PR does not:

• Change example behavior
• Add new examples
• Modify runtime logic
• Change public APIs

It only ensures existing checkpoint-continuation coverage is exercised during normal repository validation.

Tier 2 Coverage Impact

This removes a validation gap identified during the Tier 2 audit by bringing an existing checkpoint-continuation package into the standard validation workflow.