feat(ui): navigate trace steps with keyboard and remove indirect editor focus - #11005

Recreated in the upstream repository by OpenCode (gpt-5.6-sol) on behalf of @hi-ogawa to test stacked PR behavior. This automated recreation has not been human-reviewed.\n> Original PR: #10986

Description

• closes Support keyboard navigation between trace view step selection #10985

Trace steps currently require repeated clicks of each steps to go through and this can be cumbersome for quick skim.

This PR adds standard keyboard arrow/home/end navigation so it allows going up and down easily.

One fundamental editor behavior change is required for this, which is now "open editor" actions won't automatically move the browser focus to editor cursor at all. This behavior seems natural since if it's static report view, then moving the cursor there is meaningless, and even if it's editable watch UI, I don't think people would immediately start typing after such indirect cursor focus jump where you don't even know which column it jumped to.

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