docs: define intercept coroutine scope

[cayasde]

What changed

• Documented that controlled interception supports yields in the captured coroutine.
• Documented that child and independent coroutines remain outside the capture scope.
• Removed the completed TODO checklist.

Why

The coroutine boundary is intentional: recursive capture of task.spawn descendants would require scheduler-wide context propagation and is not part of the library's contract.

Impact

Users can use task.wait() within the captured execution, while coordinating child tasks separately.

Validation

npm run check

npm test