[aniruddh18122006-cyber]

Summary

Fixes the image format mismatch when editing images with uppercase file extensions.

Changes

• Normalize saved image extensions to lowercase.
• Normalize JPEG MIME types before canvas encoding.
• Validate the encoded image blob before uploading it.
• Add regression test cases for uppercase .JPG and .JPEG filenames.

Testing

Testing results will be updated after verification.

Fixes #3424

[skjnldsv]

Hi, this looks like AI. If so, please follow our AI conduct and mention the assisted-by tag on your commits and in this pr body.
Please also fix the failing ci checks: DCO and Conventional commits by adjusting the commit title using conventional commits rules and by signing-off your commits 🙏😊

[skjnldsv]

Thanks a lot! master doesn't take changes any more, so I took your fix over to stable35 in #3450, with you as co-author. I kept the extension as it is, as lowercasing it saved ABC1234.JPG as a new ABC1234.jpg.