test: add TypeScript FFI surface coverage

[TheHypnoo]

Summary

Adds explicit TypeScript FFI surface coverage accounting and splits the generated coverage inventory into domain-focused parity fixtures.

Changes

• Reworks test-coverage/audit.sh to report TypeScript, Rust, and combined FFI coverage separately.
• Adds a regenerable TypeScript FFI surface inventory split across runtime core, runtime UI/platform, stdlib core, stdlib IO/framework, and stdlib integrations.
• Adds test_compat_core_surface.ts with deterministic behavioral parity checks for core JS runtime features.
• Updates parity output normalization for Node's --experimental-strip-types warning.
• Regenerates test-coverage/COVERAGE.md with 100% TypeScript FFI surface coverage under the audit metric.

Related issue

n/a

Follow-up issues

• Add behavioral TS parity tests for runtime core FFI surface #695
• Add behavioral TS parity tests for stdlib core utilities #696
• Add behavioral TS tests for stdlib IO and framework APIs #697
• Add behavioral TS tests for stdlib external integrations #698
• Add behavioral coverage for runtime UI and platform FFI surface #699

Test plan

• ./test-coverage/regen_ts_surface_inventory.py
• ./test-coverage/audit.sh --markdown
• ./run_parity_tests.sh --filter test_ffi_surface
• ./run_parity_tests.sh --filter test_compat_core_surface
• git diff --check

Notes

This improves FFI surface coverage accounting. The inventory entries are not a replacement for deeper semantic compatibility tests; they are intended to provide a complete map that can be converted into behavioral parity fixtures over follow-up work.

Checklist

• I have NOT bumped the workspace version or edited CLAUDE.md / CHANGELOG.md
• My commit follows the loose conventional prefix style used in the log
• I've read CONTRIBUTING.md and agree to the Code of Conduct