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/storage/IndexedDBContext.ts

@@ -19,7 +19,7 @@ import { IStore } from './IStore';
  */
 export class IndexedDBContext {
   private static readonly DB_NAME = 'CalendarDB';
-  private static readonly DB_VERSION = 2;
+  private static readonly DB_VERSION = 3; // Bumped for audit store
   static readonly QUEUE_STORE = 'operationQueue';
   static readonly SYNC_STATE_STORE = 'syncState';