Bound tool index process cleanup

[rudijetson]

Summary

• terminate timed-out stack discovery processes and close inherited stdio/readline handles
• escalate to SIGKILL after a bounded grace period when a child ignores SIGTERM
• add a PID-based orphan-process regression and bump the CLI to 1.10.21

Live defect

A completed full tool-index rebuild wrote a valid cache but the CLI stayed alive for more than 16 minutes because a timed-out discovery child retained process handles.

Verification

• red regression reproduced the lingering child
• focused tests: 2/2 passing, including five consecutive orphan-process checks
• full CLI suite: 662/662 passing
• build and git diff check passing
• configured SWE debt scan: 0 findings
• npm pack dry run: 1.10.21, six files
• deterministic rebuild hash verified