feat(ui): highlight editor source locations

[hi-ogawa]

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: #10989

Description

Currently UI has action to open code view with a line information (e.g. artifact link, error link, trace step), but the opened code editor only shows a fainted cursor and it has a very limited UX value.

This PR adds an editor line highlight style to make the active line obvious.

📸 Demo

Tested on merge report run https://github.com/vitest-dev/vitest/actions/runs/32203733745/job/95924081848

Screen.Recording.2026-08-19.at.11.33.17.mov

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