Adds the TypeScript coordinator runtime to @apache-airflow/ts-sdk, the
follow-up to #67908 (TypeScript task SDK public interface). This lets Airflow
execute registered TypeScript task handlers through a bundled Node.js entrypoint.

• Adds the coordinator runtime that speaks the supervisor wire protocol
  (length-prefixed msgpack frames) over the --comm and --logs sockets:
  connects, receives the task startup message, dispatches to the registered
  handler for the Dag/task pair, and reports the terminal task state.
• Adds TaskClient-backed task-time data access: Variables (get / getOrThrow),
  XCom (get / set, including the automatic return_value push for non-undefined
  handler returns), and Connections.
• Adds cooperative cancellation via ctx.signal (AbortSignal); SIGTERM/SIGINT
  abort the signal with a grace period before force-exit.
• Adds generated supervisor wire types (src/generated/supervisor.ts) plus a
  generate:supervisor script, and a ./coordinator package export subpath.
• Adds an example/ showing a Python stub Dag + TypeScript handlers, bundled
  with esbuild, and documents the bundle layout and Airflow coordinator config.

This is intentionally still Python-stub-Dag mode: TypeScript Dag declaration is
not introduced here. TypeScript registers handlers for Dag/task IDs declared by
Python stub tasks. The example bundles with esbuild and writes
airflow-metadata.yaml manually; folding metadata generation into the build
script is left to a separate follow-up.

Testing performed:

• Unit tests and full e2e test with the airflow coordinator. Readme to run tests is available under examples.

Next steps

• Combine airflow-metadata.yml with the .mjs file and introduce a ts pack tool.