feat: expose pulled secrets as json output

[BK1031]

• Exposes pulled Vault secrets as a secrets_json action output for later step and action inputs.
• Parses simple and multiline GitHub env-file values into the JSON output.
• Extends the smoke workflow to verify both env var and step output consumption paths.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Parse heredoc syntax only before the value

When Vault returns a valid single-line env-file entry whose secret value contains << (for example TOKEN=abc<<def), GitHub still treats it as the documented name=value form, but this parser enters the multiline branch, turns the key into TOKEN=abc, and consumes following lines until def. That makes secrets_json omit or corrupt this and subsequent secrets even though they are correctly appended to GITHUB_ENV; the multiline check should only match the NAME<<DELIMITER header form, not any occurrence of << in the line.

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