Refactors calendar project structure and build configuration

Consolidates V2 codebase into main project directory
Updates build script to support simplified entry points
Removes redundant files and cleans up project organization

Simplifies module imports and entry points for calendar application

src/core/IGroupingStore.ts

@@ -0,0 +1,4 @@
+export interface IGroupingStore<T = unknown> {
+  readonly type: string;
+  getByIds(ids: string[]): T[];
+}