[P2] Validate & harden Java/JS adapters end-to-end

[pro-utkarshM]

Problem

Java (JUnit) and JS/TS (Jest) adapters are marked Beta and unproven end-to-end (generate→write→run→parse).

Tasks

• End-to-end test each adapter on a tiny sample project.
• Verify result parsing for non-pytest runners.
• Fixtures/mocks per framework.
• Promote beta→stable in README once green.

Acceptance

Each adapter generates and runs passing tests on its sample project in CI.