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/storage/BaseEntityService.ts

@@ -1,6 +1,7 @@
 import { ISync, EntityType, SyncStatus } from '../types/CalendarTypes';
 import { IEntityService } from './IEntityService';
 import { SyncPlugin } from './SyncPlugin';
+import { IndexedDBContext } from './IndexedDBContext';
 
 /**
  * BaseEntityService<T extends ISync> - Abstract base class for all entity services
@@ -13,6 +14,7 @@ import { SyncPlugin } from './SyncPlugin';
  * - Generic CRUD operations (get, getAll, save, delete)
  * - Sync status management (delegates to SyncPlugin)
  * - Serialization hooks (override in subclass if needed)
+ * - Lazy database access via IndexedDBContext
  *
  * SUBCLASSES MUST IMPLEMENT:
  * - storeName: string (IndexedDB object store name)
@@ -27,6 +29,7 @@ import { SyncPlugin } from './SyncPlugin';
  * - Type safety: Generic T ensures compile-time checking
  * - Pluggable: SyncPlugin can be swapped for testing/different implementations
  * - Open/Closed: New entities just extend this class
+ * - Lazy database access: db requested when needed, not at construction time
  */
 export abstract class BaseEntityService<T extends ISync> implements IEntityService<T> {
   // Abstract properties - must be implemented by subclasses
@@ -36,17 +39,25 @@ export abstract class BaseEntityService<T extends ISync> implements IEntityServi
   // Internal composition - sync functionality
   private syncPlugin: SyncPlugin<T>;
 
-  // Protected database instance - accessible to subclasses
-  protected db: IDBDatabase;
+  // IndexedDB context - provides database connection
+  private context: IndexedDBContext;
 
   /**
-   * @param db - IDBDatabase instance (injected dependency)
+   * @param context - IndexedDBContext instance (injected dependency)
    */
-  constructor(db: IDBDatabase) {
-    this.db = db;
+  constructor(context: IndexedDBContext) {
+    this.context = context;
     this.syncPlugin = new SyncPlugin<T>(this);
   }
 
+  /**
+   * Get IDBDatabase instance (lazy access)
+   * Protected getter accessible to subclasses and methods in this class
+   */
+  protected get db(): IDBDatabase {
+    return this.context.getDatabase();
+  }
+
   /**
    * Serialize entity before storing in IndexedDB
    * Override in subclass if entity has Date fields or needs transformation