Let strikethrough work in the theme colors that gocui draws

Config.md lists strikethrough as a modifier for theme colors, but only
GetTextStyle knows it. GetGocuiStyle turns an unknown name into white,
and white OR-ed with a palette color is white. So if you set a border
color to [red, strikethrough], you get a white border without
strikethrough. The same goes for the parts of the selected line,
options text and default text colors that gocui draws.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

pkg/theme/gocui.go

@@ -7,18 +7,19 @@ import (
 )
 
 var gocuiColorMap = map[string]gocui.Attribute{
-	"default":   gocui.ColorDefault,
-	"black":     gocui.ColorBlack,
-	"red":       gocui.ColorRed,
-	"green":     gocui.ColorGreen,
-	"yellow":    gocui.ColorYellow,
-	"blue":      gocui.ColorBlue,
-	"magenta":   gocui.ColorMagenta,
-	"cyan":      gocui.ColorCyan,
-	"white":     gocui.ColorWhite,
-	"bold":      gocui.AttrBold,
-	"reverse":   gocui.AttrReverse,
-	"underline": gocui.AttrUnderline,
+	"default":       gocui.ColorDefault,
+	"black":         gocui.ColorBlack,
+	"red":           gocui.ColorRed,
+	"green":         gocui.ColorGreen,
+	"yellow":        gocui.ColorYellow,
+	"blue":          gocui.ColorBlue,
+	"magenta":       gocui.ColorMagenta,
+	"cyan":          gocui.ColorCyan,
+	"white":         gocui.ColorWhite,
+	"bold":          gocui.AttrBold,
+	"reverse":       gocui.AttrReverse,
+	"underline":     gocui.AttrUnderline,
+	"strikethrough": gocui.AttrStrikeThrough,
 }
 
 // GetGocuiAttribute gets the gocui color attribute from the string

pkg/theme/gocui_test.go

@@ -0,0 +1,38 @@
+package theme
+
+import (
+	"testing"
+
+	"github.com/jesseduffield/lazygit/pkg/gocui"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGetGocuiStyle(t *testing.T) {
+	scenarios := []struct {
+		name     string
+		keys     []string
+		expected gocui.Attribute
+	}{
+		{
+			name:     "named color",
+			keys:     []string{"red"},
+			expected: gocui.ColorRed,
+		},
+		{
+			name:     "named color with modifiers",
+			keys:     []string{"red", "bold", "underline"},
+			expected: gocui.ColorRed | gocui.AttrBold | gocui.AttrUnderline,
+		},
+		{
+			name:     "strikethrough",
+			keys:     []string{"red", "strikethrough"},
+			expected: gocui.ColorRed | gocui.AttrStrikeThrough,
+		},
+	}
+
+	for _, scenario := range scenarios {
+		t.Run(scenario.name, func(t *testing.T) {
+			assert.Equal(t, scenario.expected, GetGocuiStyle(scenario.keys))
+		})
+	}
+}