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/workers/DataSeeder.ts

@@ -0,0 +1,103 @@
+import { IApiRepository } from '../repositories/IApiRepository';
+import { IEntityService } from '../storage/IEntityService';
+
+/**
+ * DataSeeder - Orchestrates initial data loading from repositories into IndexedDB
+ *
+ * ARCHITECTURE:
+ * - Repository (Mock/Api): Fetches data from source (JSON file or backend API)
+ * - DataSeeder (this class): Orchestrates fetch + save operations
+ * - Service (EventService, etc.): Saves data to IndexedDB
+ *
+ * SEPARATION OF CONCERNS:
+ * - Repository does NOT know about IndexedDB or storage
+ * - Service does NOT know about where data comes from
+ * - DataSeeder connects them together
+ *
+ * POLYMORPHIC DESIGN:
+ * - Uses arrays of IEntityService<any>[] and IApiRepository<any>[]
+ * - Matches services with repositories using entityType property
+ * - Open/Closed Principle: Adding new entity requires no code changes here
+ *
+ * USAGE:
+ * Called once during app initialization in index.ts:
+ * 1. IndexedDBService.initialize() - open database
+ * 2. dataSeeder.seedIfEmpty() - load initial data if needed
+ * 3. CalendarManager.initialize() - start calendar
+ *
+ * NOTE: This is for INITIAL SEEDING only. Ongoing sync is handled by SyncManager.
+ */
+export class DataSeeder {
+  constructor(
+    // Arrays injected via DI - automatically includes all registered services/repositories
+    private services: IEntityService<any>[],
+    private repositories: IApiRepository<any>[]
+  ) {}
+
+  /**
+   * Seed all entity stores if they are empty
+   * Runs on app initialization to load initial data from repositories
+   *
+   * Uses polymorphism: loops through all services and matches with repositories by entityType
+   */
+  async seedIfEmpty(): Promise<void> {
+    console.log('[DataSeeder] Checking if database needs seeding...');
+
+    try {
+      // Loop through all entity services (Event, Booking, Customer, Resource, etc.)
+      for (const service of this.services) {
+        // Find matching repository for this service based on entityType
+        const repository = this.repositories.find(repo => repo.entityType === service.entityType);
+
+        if (!repository) {
+          console.warn(`[DataSeeder] No repository found for entity type: ${service.entityType}, skipping`);
+          continue;
+        }
+
+        // Seed this entity type
+        await this.seedEntity(service.entityType, service, repository);
+      }
+
+      console.log('[DataSeeder] Seeding complete');
+    } catch (error) {
+      console.error('[DataSeeder] Seeding failed:', error);
+      throw error;
+    }
+  }
+
+  /**
+   * Generic method to seed a single entity type
+   *
+   * @param entityType - Entity type ('Event', 'Booking', 'Customer', 'Resource')
+   * @param service - Entity service for IndexedDB operations
+   * @param repository - Repository for fetching data
+   */
+  private async seedEntity<T>(
+    entityType: string,
+    service: IEntityService<any>,
+    repository: IApiRepository<T>
+  ): Promise<void> {
+    // Check if store is empty
+    const existing = await service.getAll();
+
+    if (existing.length > 0) {
+      console.log(`[DataSeeder] ${entityType} store already has ${existing.length} items, skipping seed`);
+      return;
+    }
+
+    console.log(`[DataSeeder] ${entityType} store is empty, fetching from repository...`);
+
+    // Fetch from repository (Mock JSON or backend API)
+    const data = await repository.fetchAll();
+
+    console.log(`[DataSeeder] Fetched ${data.length} ${entityType} items, saving to IndexedDB...`);
+
+    // Save each entity to IndexedDB
+    // Note: Entities from repository should already have syncStatus='synced'
+    for (const entity of data) {
+      await service.save(entity);
+    }
+
+    console.log(`[DataSeeder] ${entityType} seeding complete (${data.length} items saved)`);
+  }
+}