Disable brush in merge mode

[grittaweisheit]

This PR disables the brush when merger mode is enabled in a hybrid tracing.

URL of deployed dev instance (used for testing):

• https://disablebrushinmergemode.webknossos.xyz

Steps to test:

• open a hybrid tracing
• select the brush tool
• enable merger mode
• the tool should change to "move" and the brush button should be disabled
• disable merger mode
• the brush should be available again

Issues:

• fixes Disable brush in hybrid tracings when merge mode is activated #4757

---

• Updated (unreleased) changelog
• Updated (unreleased) migration guide if applicable
• Updated documentation if applicable
• Adapted wk-connect if datastore API changes
• Needs datastore update after deployment
• Ready for review

[daniel-wer]

Nice work 👍 I think a tooltip explaining why the buttons are disabled (in case they are) would be helpful to users. Otherwise they are left wondering why they cannot volume annotate. Message could be "Volume annotation is disabled while the merger mode is active." or something to that effect.

[daniel-wer]

The TRACE tool can also be used to volume annotate. It should be disabled in the same way.

[daniel-wer]

I noticed that the button disabled style was broken for the dark theme header (not your fault!), because we overwrote some color values there and fixed that quickly, hope that is alright with you. Now disabled buttons are grayed out as usual and can be recognized without hovering :)

[grittaweisheit]

Thanks a lot for fixing the button style!

I added the tooltip and disabled the trace tool as well :)

[daniel-wer]

Very nice, one small suggestion and then LGTM 👍