[WIP] adapt to hi-dpi screen

[fm3]

URL of deployed dev instance (used for testing):

• https://___.webknossos.xyz

TODO

• [ ] Make this opt-in (e.g. make the “Ultra“ settings in GPU Utilization menu “Ultra (hidpi)” (if available) and only use devicePixelRatio then)
• [ ] CI – Cannot read properties of undefined (reading 'devicePixelRatio')

Steps to test:

• abc

Issues:

• fixes #

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(Please delete unneeded items, merge only when none are left open)

• [ ] Updated (unreleased) changelog
• [ ] Updated (unreleased) migration guide if applicable
• [ ] Updated documentation if applicable
• [ ] Adapted wk-connect if datastore API changes
• [ ] Adapted wk-libs python client if relevant API parts change
• [ ] Needs datastore update after deployment
• [ ] Ready for review