theme: build out the theme engine core with resolve pipeline

crates/theme/src/presets.rs

@@ -0,0 +1,23 @@
+//! Built-in `ThemeDefinition` presets (D11).
+
+use crate::definition::ThemeDefinition;
+
+const TOKYO_NIGHT: &str = include_str!("../presets/tokyo-night.toml");
+
+pub fn preset_names() -> &'static [&'static str] {
+    &["tokyo-night"]
+}
+
+/// Parses the named preset.
+pub fn builtin(name: &str) -> Option<ThemeDefinition> {
+    match name {
+        "tokyo-night" => match ThemeDefinition::parse_toml(TOKYO_NIGHT) {
+            Ok(def) => Some(def),
+            Err(err) => {
+                eprintln!("bundled preset tokyo-night failed to parse: {err}");
+                None
+            }
+        },
+        _ => None,
+    }
+}