update thumbnail, allow user to choose output format

[kouz75]

Add output format support to thumbnail URLs

• Add optional format parameter to ThumbnailHelper, ImageExtension, and the thumbnail() Twig function
• Encode the output format as a filename suffix in the URL (e.g. image.jpg.avif) instead of in the param string
• Parse the format suffix in ImageController to set Glide's fm parameter and resolve the correct source file
• Backward compatible: URLs without a format suffix continue to work unchanged

Update thumbnail file path in Twig and filesystem to match image URL structure, allowing Apache/Nginx to serve them directly without any PHP call

[Vondry]

As a general question - is there a command that would "warm up" thumbnail cache so that even first user can benefit from fast loading image?

[kouz75]

There is no command for that yet.
One way to fix this is to add a new command that parses all media files (or the content) and generates their thumbnails. The thumbnail settings can be defined in theme.yaml or passed as parameters to the command.

This command may generate a lot of thumbnails that will never be displayed on the website.