Add TypeScript unit test suite for the Push3 transpiler using Node's
built-in test runner (node:test) with tsx. 47 tests across 12 suites
covering parser, stack underflow/overflow, EXEC.IF balanced/unbalanced/
nested branching, arithmetic, boolean ops, name binding, and integration.
Update CI to run `npm test` (which now includes unit tests + existing
bash tests) and scope transpiler-tests step to only trigger on changes
to tools/push3-transpiler/**.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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