[codex] isolate Tree-sitter mutation parsing

[greenthree]

What changed

• Move Tree-sitter C++ mutation parsing into the shipped mutation_parser_worker.py subprocess.
• Reuse shared process control for bounded output, timeout, cancellation, resource limits, temporary working directory, and descendant cleanup.
• Validate the worker protocol, parser identity, source hash, candidate spans, positions, and count before accepting a plan; retain the previous evidence on parser/infrastructure failure.
• Reuse the same parser worker from doctor, forward mutation deadlines/cancellation, and include the worker in npm packaging and documentation.

Why

Native Tree-sitter bindings should not run in the long-lived Core process. A bounded worker keeps parser crashes, malformed protocol output, resource exhaustion, and cancellation isolated while preserving deterministic mutation IDs and fail-closed behavior.

Validation

• tests.test_mutation_syntax: 15 passed
• tests.test_mutation: 24 passed
• tests.test_core + tests.test_npm_packages: 49 passed
• Python dependency audit: 12 dependencies, 0 vulnerabilities
• clean-install delivery flow: passed (probhub 223 files, compatibility package 5 files)
• npm run pack:check: passed
• npm run release:check: passed
• Skill validation and git diff --check: passed
• phtest nine-problem lint: passed

The full npm run check was attempted but its npm test phase exceeded the 15-minute local timeout in an unrelated long-running interactive fixture; the residual test tree was terminated and no test processes remained.

Scope

This PR does not add typeid(type) compatibility, WebUI integration, Checker/Interactor integration, Legacy support, or a mutation hard gate for build.