fix(tui): tighten zebra row contrast for Tokyo Night and Gruvbox

Previous ZebraBg was too far from Bg, washing out text on those
themes. Reduced to a 2-step shift for subtle row alternation.

internal/tui/theme.go

@@ -78,7 +78,7 @@ var themeTokyoNight = Theme{
 	Info:       "#7aa2f7",
 	Accent:     "#7dcfff",
 	Purple:     "#bb9af7",
-	ZebraBg:    "#1e1f2b",
+	ZebraBg:    "#1c1d28",
 	SelectedFg: "#c0caf5",
 	SelectedBg: "#292e42",
 }
@@ -98,7 +98,7 @@ var themeGruvbox = Theme{
 	Info:       "#83a598",
 	Accent:     "#8ec07c",
 	Purple:     "#d3869b",
-	ZebraBg:    "#2e2c2a",
+	ZebraBg:    "#2a2a2a",
 	SelectedFg: "#fbf1c7",
 	SelectedBg: "#504945",
 }