fix(eval): make process termination work on Windows

[jjj-n]

Summary

• Add a shared Eval process-termination helper with native graceful Windows stops and taskkill.exe tree escalation for forced cleanup.
• Use the helper for harness trials, external subject wrappers, and preflight timeout/cancellation paths.

Fixes#3892.

Verification

• npm run lint passed.
• npm run format:check passed.
• npm --workspace @maka/eval run typecheck passed.
• npm --workspace @maka/eval run build passed.
• npx knip --workspace apps/desktop passed.
• npx knip --workspace packages/ui passed.
• node --test packages/eval/dist/__tests__/process-termination.test.js packages/eval/dist/__tests__/install-preflight.test.js passed: 10 passed, 3 skipped because this Windows environment does not grant symlink/permission prerequisites.
• Root npm run typecheck is blocked by existing @maka/ui errors for settledText, autoScroll, and trailingAction; Eval and its dependencies typecheck successfully.
• Root npm run build reaches the same existing @maka/ui type errors after building Eval and its dependencies.
• The full Eval suite was not reported as passing because this Windows environment exposes existing POSIX/shebang, symlink, and path assumptions in unrelated tests.

AI use

• No generative tool made a substantive contribution
• Generative tooling made a substantive contribution

Tool(s) and scope: Codex implemented the process-termination helper, call-site updates, regression tests, and verification. The human contributor of record reviews the implementation for correctness and licensing.

Checklist

• Tests cover the change and fail without it
• Lint, format, typecheck and the affected suites pass locally

Does this PR entail a change in behavior?

• Yes - described under Summary above
• No