feat: respect env var `$SOURCE_DATE_EPOCH` when generating SBOM

## Is your feature request related to a problem? Please describe.

The timestamp should be set to $SOURCE_DATE_EPOCH env var, so that builds are deterministic and can be reproduced at some point in the future.

## Describe the solution you'd like

More explanation here: https://reproducible-builds.org/docs/source-date-epoch/

Start by locating the SBOM generation entry point and the code that assigns its timestamp. Read the linked SOURCE_DATE_EPOCH guidance to confirm the expected environment-variable behavior, then verify that generated SBOMs use that value and remain deterministic across repeated builds.

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