Separate resolved theme values from configuration resolution

Cargo.lock

@@ -1681,6 +1681,7 @@ dependencies = [
 name = "ferese-config"
 version = "0.1.0"
 dependencies = [
+ "ferese-theme-model",
  "jiff",
  "kdl",
  "serde",
@@ -1811,6 +1812,13 @@ dependencies = [
  "wayland-client",
 ]
 
+[[package]]
+name = "ferese-theme-model"
+version = "0.1.0"
+dependencies = [
+ "serde",
+]
+
 [[package]]
 name = "feresectl"
 version = "0.1.0"