Use safe RUNNER_TEMP paths in generated workflow scripts (#54303)

* Initial plan

* Use safe runner temp paths in generated scripts

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* docs(adr): add draft ADR-54303 for runtime path resolution in generated workflows

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* Fail closed for runner temp safety validation

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

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Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>
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Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>