Improve handling of large video file attachments

[ianrahman]

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• I have read the README and CONTRIBUTING documents
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Contributor checklist

• My commits are rebased on the latest main branch
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• My contribution is fully baked and is ready to be merged as is
• I have tested my contribution on these devices:

• iPhone 16 Pro Max, iOS 26.1 b4

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Addresses #4370

Description

• retry AVAsset exports across presets and map AVError.maximumFileSizeReached to .fileSizeTooLarge
• enforce preset dimension limits based on bitrate estimates and annotate the heuristics we rely on
• add shared helpers for export error detection and size/quality guardrails
• made media file size limits consistent and removed hardcoded calculations for static values

Testing

• Attached a large (> 100 MB) video file to a message and successfully sent to a non-dev device. Received video size was < 100 MB and video quality was significantly better than same video attached and sent with current production implementation.