feat: allow user to multi-select regions.

src/components/interfaces.ts

@@ -18,6 +18,10 @@ export interface RegionUI {
   name: string;
 }
 
+export interface RegionClickOptions {
+  shiftKey: boolean;
+}
+
 // Define resize action types
 export type ResizeAction = 'none' | 'start' | 'end';
 
@@ -39,4 +43,4 @@ export interface RegionDragState {
   initialY: number;
   initialBarNumber: number;
   initialTrackIndex: number;
-} 
+}