fix(preview): execute PreviewMapper::deleteAll()

[joshtrichards]

• Resolves: #

Summary

Fix PreviewMapper::deleteAll() so that it actually executes the generated DELETE statement. ;-)

Production code, such as preview cleanup currently removes previews individually through PreviewService::deleteAll() (which uses PreviewMapper::delete() for each one), but this mapper method is used by tests (in tearDown()) and is a no-op for any future callers.

TODO

• Backport to >=v33

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI

[joshtrichards]

/backport to stable34

[joshtrichards]

/backport to stable33