Adds comprehensive mock data repositories and seeding infrastructure

Implements polymorphic data seeding mechanism for initial application setup

- Adds Mock repositories for Event, Booking, Customer, and Resource entities
- Creates DataSeeder to automatically populate IndexedDB from JSON sources
- Enhances index.ts initialization process with data seeding step
- Adds mock JSON data files for comprehensive test data

Improves offline-first and development testing capabilities

src/storage/IEntityService.ts

@@ -4,13 +4,13 @@ import { ISync, EntityType, SyncStatus } from '../types/CalendarTypes';
  * IEntityService<T> - Generic interface for entity services with sync capabilities
  *
  * All entity services (Event, Booking, Customer, Resource) implement this interface
- * to enable polymorphic sync status management in SyncManager.
+ * to enable polymorphic operations across different entity types.
  *
  * ENCAPSULATION: Services encapsulate sync status manipulation.
  * SyncManager does NOT directly manipulate entity.syncStatus - it delegates to the service.
  *
- * POLYMORFI: SyncManager works with Array<IEntityService<any>> and uses
- * entityType property for runtime routing, avoiding switch statements.
+ * POLYMORPHISM: Both SyncManager and DataSeeder work with Array<IEntityService<any>>
+ * and use entityType property for runtime routing, avoiding switch statements.
  */
 export interface IEntityService<T extends ISync> {
   /**
@@ -19,6 +19,30 @@ export interface IEntityService<T extends ISync> {
    */
   readonly entityType: EntityType;
 
+  // ============================================================================
+  // CRUD Operations (used by DataSeeder and other consumers)
+  // ============================================================================
+
+  /**
+   * Get all entities from IndexedDB
+   * Used by DataSeeder to check if store is empty before seeding
+   *
+   * @returns Promise<T[]> - Array of all entities
+   */
+  getAll(): Promise<T[]>;
+
+  /**
+   * Save an entity (create or update) to IndexedDB
+   * Used by DataSeeder to persist fetched data
+   *
+   * @param entity - Entity to save
+   */
+  save(entity: T): Promise<void>;
+
+  // ============================================================================
+  // SYNC Methods (used by SyncManager)
+  // ============================================================================
+
   /**
    * Mark entity as successfully synced with backend
    * Sets syncStatus = 'synced' and persists to IndexedDB