Added diff rows lost their background tint, inconsistent with deleted rows

Summary

Added (+) diff lines render on the neutral theme.Surface background, while deleted lines get a color-derived tint. The result: added lines look like they have no diff highlight, in every theme. Likely an oversight rather than an intentional choice — flagging in case it wasn't.

Where

tui/ui_diff_viewer.go, uiStyleForDiffRow:

case diff.RowAdd:
    return vaxis.Style{Foreground: theme.Success, Background: theme.Surface}            // neutral grey
case diff.RowDelete:
    return vaxis.Style{Foreground: ..., Background: uiDiffLineBackground(theme, theme.Palette.Red)}  // red tint

The two changed-row kinds are otherwise treated consistently (delete = tinted bg + dimmed tokens; add = tinted bg + full-color tokens), so only the add background looks out of place.

History

This coincided with the syntax-highlighting commit 5a123d1 ("tui: theme and highlight ui diff rows"). Just before it, 536fc4c had:

case diff.RowAdd:
    return vaxis.Style{Foreground: theme.Success, Background: uiDiffLineBackground(theme, theme.Palette.Green)}

5a123d1 switched that background to theme.Surface; delete was left intact. Possibly a deliberate attempt to avoid syntax colors clashing with a green wash — but uiDiffLineBackground returns Tone50/Tone950 (a very faint tint), and deleted lines already render full-color/dimmed syntax over their red tint without issue, so the clash concern may not apply.

Suggested fix

Restore the green-derived background (foreground unchanged), matching the pre-5a123d1 line:

case diff.RowAdd:
    return vaxis.Style{Foreground: theme.Success, Background: uiDiffLineBackground(theme, theme.Palette.Green)}

Happy to open a PR if this wasn't intentional.

Open tui/ui_diff_viewer.go and inspect uiStyleForDiffRow, especially the diff.RowAdd case and its use of theme.Surface versus uiDiffLineBackground. Restore the green-derived background while keeping the existing foreground, then verify that added rows have a faint green tint consistently across themes.