fix(preview): Handle unique constraints violation exception

[CarlSchwan]

• Resolves: [Bug]: Integrity constraint violation: 1062 Duplicate entry for key 'previews_file_uniq_idx' #58587

Summary

Delete the preview from storage and fetch the actual one from the DB. This should not happen often.

TODO

• ...

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

[CarlSchwan]

/backport to stable34

[solracsf]

I don't think the recovery path works as written, worth review in case I'm missing a key info here.

getPreviewForSpecification() builds its WHERE clause from raw array keys used as literal column names. The caller passes 'fileId', but the column is actually file_id, that's a genuine SQL "unknown column" error, thrown before findOneQuery() ever reaches the DoesNotExistException catch this method relies on.

So the exact race this PR targets would still crash, just with a different exception than before.
😿