fix(btst): run CLI release helper from its workspace

[olliethedev]

Fixes the second CLI-only release failure observed in run 33449115287.

The monorepo root does not own tsx; @btst/cli does. The release job now resolves and runs the helper through the CLI workspace, and the helper resolves package metadata relative to its own module instead of the caller's working directory.

The regression test executes the exact package-scoped runner, validates direct GITHUB_OUTPUT records, and guards against restoring stdout redirection.

Validation:

• root targeted Vitest: 7/7
• package-scoped targeted Vitest: 7/7
• Biome
• diff check
• independent Standards and Spec reviews: no findings

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-08-31T23:14:37.925585Z	296f27a	PR opened

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