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/audit/AuditService.ts

@@ -0,0 +1,177 @@
+import { BaseEntityService } from '../BaseEntityService';
+import { IndexedDBContext } from '../IndexedDBContext';
+import { IAuditEntry } from '../../types/AuditTypes';
+import { EntityType, IEventBus } from '../../types/CalendarTypes';
+import { CoreEvents } from '../../constants/CoreEvents';
+
+/**
+ * AuditService - Entity service for audit entries
+ *
+ * RESPONSIBILITIES:
+ * - Store audit entries in IndexedDB
+ * - Listen for ENTITY_SAVED/ENTITY_DELETED events
+ * - Create audit entries for all entity changes
+ * - Emit AUDIT_LOGGED after saving (for SyncManager to listen)
+ *
+ * OVERRIDE PATTERN:
+ * - Overrides save() to NOT emit events (prevents infinite loops)
+ * - AuditService saves audit entries without triggering more audits
+ *
+ * EVENT CHAIN:
+ * Entity change → ENTITY_SAVED/DELETED → AuditService → AUDIT_LOGGED → SyncManager
+ */
+export class AuditService extends BaseEntityService<IAuditEntry> {
+  readonly storeName = 'audit';
+  readonly entityType: EntityType = 'Audit';
+
+  // Hardcoded userId for now - will come from session later
+  private static readonly DEFAULT_USER_ID = '00000000-0000-0000-0000-000000000001';
+
+  constructor(context: IndexedDBContext, eventBus: IEventBus) {
+    super(context, eventBus);
+    this.setupEventListeners();
+  }
+
+  /**
+   * Setup listeners for ENTITY_SAVED and ENTITY_DELETED events
+   */
+  private setupEventListeners(): void {
+    // Listen for entity saves (create/update)
+    this.eventBus.on(CoreEvents.ENTITY_SAVED, (event: Event) => {
+      const detail = (event as CustomEvent).detail;
+      this.handleEntitySaved(detail);
+    });
+
+    // Listen for entity deletes
+    this.eventBus.on(CoreEvents.ENTITY_DELETED, (event: Event) => {
+      const detail = (event as CustomEvent).detail;
+      this.handleEntityDeleted(detail);
+    });
+  }
+
+  /**
+   * Handle ENTITY_SAVED event - create audit entry
+   */
+  private async handleEntitySaved(payload: {
+    entityType: EntityType;
+    entityId: string;
+    operation: 'create' | 'update';
+    changes: any;
+    timestamp: number;
+  }): Promise<void> {
+    // Don't audit audit entries (prevent infinite loops)
+    if (payload.entityType === 'Audit') return;
+
+    const auditEntry: IAuditEntry = {
+      id: crypto.randomUUID(),
+      entityType: payload.entityType,
+      entityId: payload.entityId,
+      operation: payload.operation,
+      userId: AuditService.DEFAULT_USER_ID,
+      timestamp: payload.timestamp,
+      changes: payload.changes,
+      synced: false,
+      syncStatus: 'pending'
+    };
+
+    await this.save(auditEntry);
+  }
+
+  /**
+   * Handle ENTITY_DELETED event - create audit entry
+   */
+  private async handleEntityDeleted(payload: {
+    entityType: EntityType;
+    entityId: string;
+    operation: 'delete';
+    timestamp: number;
+  }): Promise<void> {
+    // Don't audit audit entries (prevent infinite loops)
+    if (payload.entityType === 'Audit') return;
+
+    const auditEntry: IAuditEntry = {
+      id: crypto.randomUUID(),
+      entityType: payload.entityType,
+      entityId: payload.entityId,
+      operation: 'delete',
+      userId: AuditService.DEFAULT_USER_ID,
+      timestamp: payload.timestamp,
+      changes: { id: payload.entityId }, // For delete, just store the ID
+      synced: false,
+      syncStatus: 'pending'
+    };
+
+    await this.save(auditEntry);
+  }
+
+  /**
+   * Override save to NOT trigger ENTITY_SAVED event
+   * Instead, emits AUDIT_LOGGED for SyncManager to listen
+   *
+   * This prevents infinite loops:
+   * - BaseEntityService.save() emits ENTITY_SAVED
+   * - AuditService listens to ENTITY_SAVED and creates audit
+   * - If AuditService.save() also emitted ENTITY_SAVED, it would loop
+   */
+  async save(entity: IAuditEntry): Promise<void> {
+    const serialized = this.serialize(entity);
+
+    return new Promise((resolve, reject) => {
+      const transaction = this.db.transaction([this.storeName], 'readwrite');
+      const store = transaction.objectStore(this.storeName);
+      const request = store.put(serialized);
+
+      request.onsuccess = () => {
+        // Emit AUDIT_LOGGED instead of ENTITY_SAVED
+        this.eventBus.emit(CoreEvents.AUDIT_LOGGED, {
+          auditId: entity.id,
+          entityType: entity.entityType,
+          entityId: entity.entityId,
+          operation: entity.operation,
+          timestamp: entity.timestamp
+        });
+        resolve();
+      };
+
+      request.onerror = () => {
+        reject(new Error(`Failed to save audit entry ${entity.id}: ${request.error}`));
+      };
+    });
+  }
+
+  /**
+   * Override delete to NOT trigger ENTITY_DELETED event
+   * Audit entries should never be deleted (compliance requirement)
+   */
+  async delete(_id: string): Promise<void> {
+    throw new Error('Audit entries cannot be deleted (compliance requirement)');
+  }
+
+  /**
+   * Get pending audit entries (for sync)
+   */
+  async getPendingAudits(): Promise<IAuditEntry[]> {
+    return this.getBySyncStatus('pending');
+  }
+
+  /**
+   * Get audit entries for a specific entity
+   */
+  async getByEntityId(entityId: string): Promise<IAuditEntry[]> {
+    return new Promise((resolve, reject) => {
+      const transaction = this.db.transaction([this.storeName], 'readonly');
+      const store = transaction.objectStore(this.storeName);
+      const index = store.index('entityId');
+      const request = index.getAll(entityId);
+
+      request.onsuccess = () => {
+        const entries = request.result as IAuditEntry[];
+        resolve(entries);
+      };
+
+      request.onerror = () => {
+        reject(new Error(`Failed to get audit entries for entity ${entityId}: ${request.error}`));
+      };
+    });
+  }
+}