Adds audit logging and sync management infrastructure

Introduces comprehensive audit trail system with:
- AuditService to track entity changes
- SyncManager for background sync of audit entries
- New CoreEvents for entity and audit tracking
- Simplified sync architecture with event-driven approach

Prepares system for enhanced compliance and change tracking

src/types/AuditTypes.ts

@@ -0,0 +1,38 @@
+import { ISync, EntityType } from './CalendarTypes';
+
+/**
+ * IAuditEntry - Audit log entry for tracking all entity changes
+ *
+ * Used for:
+ * - Compliance and audit trail
+ * - Sync tracking with backend
+ * - Change history
+ */
+export interface IAuditEntry extends ISync {
+    /** Unique audit entry ID */
+    id: string;
+
+    /** Type of entity that was changed */
+    entityType: EntityType;
+
+    /** ID of the entity that was changed */
+    entityId: string;
+
+    /** Type of operation performed */
+    operation: 'create' | 'update' | 'delete';
+
+    /** User who made the change */
+    userId: string;
+
+    /** Timestamp when change was made */
+    timestamp: number;
+
+    /** Changes made (full entity for create, diff for update, { id } for delete) */
+    changes: any;
+
+    /** Whether this audit entry has been synced to backend */
+    synced: boolean;
+
+    /** Sync status inherited from ISync */
+    syncStatus: 'synced' | 'pending' | 'error';
+}

src/types/CalendarTypes.ts

@@ -12,7 +12,7 @@ export type SyncStatus = 'synced' | 'pending' | 'error';
 /**
  * EntityType - Discriminator for all syncable entities
  */
-export type EntityType = 'Event' | 'Booking' | 'Customer' | 'Resource';
+export type EntityType = 'Event' | 'Booking' | 'Customer' | 'Resource' | 'Audit';
 
 /**
  * ISync - Interface composition for sync status tracking