theme: add linux system theme sources

crates/theme/src/system.rs

@@ -14,10 +14,14 @@ pub struct AccessibilityPreferences {
 
 /// Which adapter produced a [`SystemTheme`].
 #[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
+#[cfg_attr(not(target_os = "linux"), allow(dead_code))]
 pub enum SourceKind {
     #[default]
     Fallback,
     Macos,
+    Omarchy,
+    Kde,
+    Gnome,
 }
 
 impl SourceKind {
@@ -25,6 +29,9 @@ impl SourceKind {
         match self {
             Self::Fallback => "neutral fallback",
             Self::Macos => "macOS (NSColor)",
+            Self::Omarchy => "Omarchy (colors.toml)",
+            Self::Kde => "KDE (kdeglobals)",
+            Self::Gnome => "GNOME (portal)",
         }
     }
 }