refactor: isolate workspace cleanup guard

[sunsunsun-java]

Summary

• rename execution-convergence to a single-purpose workspace cleanup guard
• remove benchmark-only profiles, active evidence projection, model hints, failure intervention, and validation timeout policy from the production package
• preserve workspace provenance and deletion confirmation across Pi tool and settlement lifecycle hooks
• add independent success, refusal, cancellation, and exception regression tests
• update README runtime and repository-structure documentation

Validation

• bun run check
• bun run test: 868 Node tests and 30 Vitest tests passed
• workspace cleanup guard: 16 focused tests passed
• npm pack --dry-run --json confirms only the new production guard is published

Closes #126