feat(theme): add catppuccin themes with transparency and 256-color support

Add a theme package providing all four catppuccin flavors (mocha,
frappe, macchiato, latte) mapped to the xterm-256 palette. Themes are
selected with -theme or the CTOP_THEME environment variable; -i inverts
the flavor. Background slots use the terminal's native color for
transparency (opt out with -solid / CTOP_SOLID), and termbox is switched
to Output256 so colors render correctly. Replace hardcoded colors in the
compact and single views with ctheme portrait slots.

cwidgets/single/io.go

@@ -5,6 +5,7 @@ import (
 	"strings"
 
 	"github.com/bcicen/ctop/cwidgets"
+	"github.com/bcicen/ctop/theme"
 	ui "github.com/gizak/termui"
 )
 
@@ -26,13 +27,13 @@ func NewIO() *IO {
 	read.Title = "READ"
 	read.Height = 1
 	read.Data = io.readHist.Data
-	read.LineColor = ui.ColorGreen
+	read.LineColor = theme.Attr("io.read")
 
 	write := ui.NewSparkline()
 	write.Title = "WRITE"
 	write.Height = 1
 	write.Data = io.writeHist.Data
-	write.LineColor = ui.ColorYellow
+	write.LineColor = theme.Attr("io.write")
 
 	io.Lines = []ui.Sparkline{read, write}
 	return io