Refactors calendar data management and sync infrastructure

Introduces comprehensive data management system for calendar V2
- Adds IndexedDB storage with pluggable entity services
- Implements EventBus for decoupled event communication
- Creates data seeding mechanism for initial application setup
- Establishes sync and repository abstractions for flexible data handling

src/v2/constants/CoreEvents.ts

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+/**
+ * CoreEvents - Consolidated essential events for the calendar V2
+ */
+export const CoreEvents = {
+  // Lifecycle events
+  INITIALIZED: 'core:initialized',
+  READY: 'core:ready',
+  DESTROYED: 'core:destroyed',
+
+  // View events
+  VIEW_CHANGED: 'view:changed',
+  VIEW_RENDERED: 'view:rendered',
+
+  // Navigation events
+  DATE_CHANGED: 'nav:date-changed',
+  NAVIGATION_COMPLETED: 'nav:navigation-completed',
+
+  // Data events
+  DATA_LOADING: 'data:loading',
+  DATA_LOADED: 'data:loaded',
+  DATA_ERROR: 'data:error',
+
+  // Grid events
+  GRID_RENDERED: 'grid:rendered',
+  GRID_CLICKED: 'grid:clicked',
+
+  // Event management
+  EVENT_CREATED: 'event:created',
+  EVENT_UPDATED: 'event:updated',
+  EVENT_DELETED: 'event:deleted',
+  EVENT_SELECTED: 'event:selected',
+
+  // System events
+  ERROR: 'system:error',
+
+  // Sync events
+  SYNC_STARTED: 'sync:started',
+  SYNC_COMPLETED: 'sync:completed',
+  SYNC_FAILED: 'sync:failed',
+
+  // Entity events - for audit and sync
+  ENTITY_SAVED: 'entity:saved',
+  ENTITY_DELETED: 'entity:deleted',
+
+  // Rendering events
+  EVENTS_RENDERED: 'events:rendered'
+} as const;