Release jtest 0.2.1

[liufengyun]

Summary

Release jtest, jtest-python, and jtest-ruby together as 0.2.1. Date the changelog for 2026-10-18 and update the release examples. This patch release includes clean status-1 exits after failing tests and unified, versioned API documentation at jtest.jo-lang.org.

The docs manifest will be updated after the 0.2.1 documentation archive is published, so site builds only reference available release assets.

Check list

• Tests — existing conformance and documentation regression tests passed; this PR changes release metadata only.
• Update CHANGELOG.md

Validation with the CI compiler, Jo 0.14.0:

• Both runner conformance suites and python3 scripts/check-output.py passed.
• All three packages built successfully.
• Unified API documentation generated and packaged successfully.
• All seven documentation tests passed.
• Package metadata, dependency constraints, ZIP integrity, and all seven SHA-512 checksums verified.
• git diff --check passed.

Compatibility

No public API signature or runtime requirement changes. All packages remain on the 0.2 compatibility line and require Jo 0.14. The runners depend on the shared jtest 0.2 core package.