fix: terminate tool-index process trees

[rudijetson]

Summary

• launch POSIX stack servers in dedicated process groups during discovery
• converge success, error, exit, and timeout paths on one bounded cleanup routine
• close RPC resources, wait for complete process-tree exit, and escalate to SIGKILL when required
• report stack-specific cleanup failures without exposing runtime inputs
• preserve and publish the Admin Mac operational proof on the current CLI stack

Closes #17.

Verification

• focused process-tree tests: 3 passed, 0 failed
• pnpm test: 657 passed, 0 failed
• pnpm build: passed; tracked bundle reproduced cleanly after commit
• debt scan: 0 findings
• npm pack --dry-run --json: passed with 6 expected package files
• git diff --check: passed

Stack

This PR is intentionally based on fix/15-shim-validation (#16) because each CLI concern regenerates dist/index.cjs. After #16 lands, retarget this PR to main. The obsolete 1.10.12-to-1.10.15 version bump from the historical branch was not replayed.