Refactors repository layer and IndexedDB architecture

Eliminates redundant repository abstraction layer by directly using EntityService methods

Implements key improvements:
- Removes unnecessary repository wrappers
- Introduces polymorphic DataSeeder for mock data loading
- Renames IndexedDBService to IndexedDBContext
- Fixes database injection timing with lazy access pattern
- Simplifies EventManager to use services directly

Reduces code complexity and improves separation of concerns

src/workers/SyncManager.ts

@@ -1,8 +1,6 @@
 import { IEventBus, EntityType, ISync } from '../types/CalendarTypes';
 import { CoreEvents } from '../constants/CoreEvents';
-import { OperationQueue } from '../storage/OperationQueue';
-import { IQueueOperation } from '../storage/IndexedDBService';
-import { IndexedDBService } from '../storage/IndexedDBService';
+import { OperationQueue, IQueueOperation } from '../storage/OperationQueue';
 import { IApiRepository } from '../repositories/IApiRepository';
 import { IEntityService } from '../storage/IEntityService';
 
@@ -33,7 +31,6 @@ import { IEntityService } from '../storage/IEntityService';
 export class SyncManager {
   private eventBus: IEventBus;
   private queue: OperationQueue;
-  private indexedDB: IndexedDBService;
   private repositories: Map<EntityType, IApiRepository<any>>;
   private entityServices: IEntityService<any>[];
 
@@ -46,13 +43,11 @@ export class SyncManager {
   constructor(
     eventBus: IEventBus,
     queue: OperationQueue,
-    indexedDB: IndexedDBService,
     apiRepositories: IApiRepository<any>[],
     entityServices: IEntityService<any>[]
   ) {
     this.eventBus = eventBus;
     this.queue = queue;
-    this.indexedDB = indexedDB;
     this.entityServices = entityServices;
 
     // Build map: EntityType → IApiRepository