feat: Add new system for multi-selections.

crates/pikl-core/src/model/traits.rs

@@ -41,6 +41,11 @@ pub trait Menu: Send + 'static {
     /// for output and hook events.
     fn original_index(&self, filtered_index: usize) -> Option<usize>;
 
+    /// Get the JSON value of an item by its original (pre-filter)
+    /// index. Used by multi-select to retrieve selected items
+    /// that may not be in the current filtered set.
+    fn serialize_original(&self, original_index: usize) -> Option<&serde_json::Value>;
+
     /// Get the formatted display text for a filtered item,
     /// if a format template is configured. Returns None if
     /// no template is set, in which case the raw label is