refactor: thread context through publish sensitive data check

[ishwar170695]

composeFileAsByteReader used context.TODO() as a placeholder, severing
cancellation propagation. If the parent context is cancelled (e.g. Ctrl+C),
the loader call would continue running.

Threads the real ctx through preChecks -> checkForSensitiveData -> composeFileAsByteReader. No behavioral change.

[Copilot]

Pull request overview

This PR fixes context cancellation propagation during the publish pre-checks by threading the caller’s ctx through the sensitive-data scan path, replacing a context.TODO() placeholder so that a cancelled publish can properly stop loader work.

Changes:

• Pass ctx from publish into preChecks.
• Thread ctx through checkForSensitiveData into composeFileAsByteReader.
• Use the real ctx in loader.LoadWithContext instead of context.TODO().

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