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/repositories/MockCustomerRepository.ts

@@ -0,0 +1,76 @@
+import { ICustomer } from '../types/CustomerTypes';
+import { EntityType } from '../types/CalendarTypes';
+import { IApiRepository } from './IApiRepository';
+
+interface RawCustomerData {
+  id: string;
+  name: string;
+  phone: string;
+  email?: string;
+  metadata?: Record<string, any>;
+  [key: string]: unknown;
+}
+
+/**
+ * MockCustomerRepository - Loads customer data from local JSON file
+ *
+ * This repository implementation fetches mock customer data from a static JSON file.
+ * Used for development and testing instead of API calls.
+ *
+ * Data Source: data/mock-customers.json
+ *
+ * NOTE: Create/Update/Delete operations are not supported - throws errors.
+ * Only fetchAll() is implemented for loading initial mock data.
+ */
+export class MockCustomerRepository implements IApiRepository<ICustomer> {
+  public readonly entityType: EntityType = 'Customer';
+  private readonly dataUrl = 'data/mock-customers.json';
+
+  /**
+   * Fetch all customers from mock JSON file
+   */
+  public async fetchAll(): Promise<ICustomer[]> {
+    try {
+      const response = await fetch(this.dataUrl);
+
+      if (!response.ok) {
+        throw new Error(`Failed to load mock customers: ${response.status} ${response.statusText}`);
+      }
+
+      const rawData: RawCustomerData[] = await response.json();
+
+      return this.processCustomerData(rawData);
+    } catch (error) {
+      console.error('Failed to load customer data:', error);
+      throw error;
+    }
+  }
+
+  /**
+   * NOT SUPPORTED - MockCustomerRepository is read-only
+   */
+  public async sendCreate(customer: ICustomer): Promise<ICustomer> {
+    throw new Error('MockCustomerRepository does not support sendCreate. Mock data is read-only.');
+  }
+
+  /**
+   * NOT SUPPORTED - MockCustomerRepository is read-only
+   */
+  public async sendUpdate(id: string, updates: Partial<ICustomer>): Promise<ICustomer> {
+    throw new Error('MockCustomerRepository does not support sendUpdate. Mock data is read-only.');
+  }
+
+  /**
+   * NOT SUPPORTED - MockCustomerRepository is read-only
+   */
+  public async sendDelete(id: string): Promise<void> {
+    throw new Error('MockCustomerRepository does not support sendDelete. Mock data is read-only.');
+  }
+
+  private processCustomerData(data: RawCustomerData[]): ICustomer[] {
+    return data.map((customer): ICustomer => ({
+      ...customer,
+      syncStatus: 'synced' as const
+    }));
+  }
+}