Add embedded preview support for CorelDRAW (.cdr) files

[7snack7]

• Resolves: #

Summary

This pull request adds support for generating previews for CorelDRAW (.cdr) files.

Currently, CDR files are displayed with a generic icon even when they contain an embedded preview image. This change introduces a new preview provider that extracts the embedded thumbnail directly from the CDR archive.

Both modern CorelDRAW files containing previews/thumbnail.png and legacy files containing metadata/thumbnails/thumbnail.bmp are supported.

The implementation has no external dependencies and does not require ImageMagick or temporary file creation.

Tested on a production-like Nextcloud instance used within our company with real production CDR files.

TODO

• Add PHPUnit tests for the CDR preview provider.

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