theme: palette and accent colors

[practicalli-johnny]

Configure Zensical theme to have the light/dark switch mode and also set primary and accent colors.

[[project.theme.palette]] 
scheme = "default"
toggle.icon = "lucide/sun"
toggle.name = "Switch to dark mode"
primary = "color"
accent = "color"

[[project.theme.palette]]
scheme = "slate"
toggle.icon = "lucide/moon"
toggle.name = "Switch to light mode"
primary = "color"
accent = "color"