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/core/EventBus.ts

@@ -0,0 +1,174 @@
+import { IEventLogEntry, IListenerEntry, IEventBus } from '../types/CalendarTypes';
+
+/**
+ * Central event dispatcher for calendar using DOM CustomEvents
+ * Provides logging and debugging capabilities
+ */
+export class EventBus implements IEventBus {
+  private eventLog: IEventLogEntry[] = [];
+  private debug: boolean = false;
+  private listeners: Set<IListenerEntry> = new Set();
+
+  // Log configuration for different categories
+  private logConfig: { [key: string]: boolean } = {
+    calendar: true,
+    grid: true,
+    event: true,
+    scroll: true,
+    navigation: true,
+    view: true,
+    default: true
+  };
+
+  /**
+   * Subscribe to an event via DOM addEventListener
+   */
+  on(eventType: string, handler: EventListener, options?: AddEventListenerOptions): () => void {
+    document.addEventListener(eventType, handler, options);
+
+    // Track for cleanup
+    this.listeners.add({ eventType, handler, options });
+
+    // Return unsubscribe function
+    return () => this.off(eventType, handler);
+  }
+
+  /**
+   * Subscribe to an event once
+   */
+  once(eventType: string, handler: EventListener): () => void {
+    return this.on(eventType, handler, { once: true });
+  }
+
+  /**
+   * Unsubscribe from an event
+   */
+  off(eventType: string, handler: EventListener): void {
+    document.removeEventListener(eventType, handler);
+
+    // Remove from tracking
+    for (const listener of this.listeners) {
+      if (listener.eventType === eventType && listener.handler === handler) {
+        this.listeners.delete(listener);
+        break;
+      }
+    }
+  }
+
+  /**
+   * Emit an event via DOM CustomEvent
+   */
+  emit(eventType: string, detail: unknown = {}): boolean {
+    // Validate eventType
+    if (!eventType) {
+      return false;
+    }
+
+    const event = new CustomEvent(eventType, {
+      detail: detail ?? {},
+      bubbles: true,
+      cancelable: true
+    });
+
+    // Log event with grouping
+    if (this.debug) {
+      this.logEventWithGrouping(eventType, detail);
+    }
+
+    this.eventLog.push({
+      type: eventType,
+      detail: detail ?? {},
+      timestamp: Date.now()
+    });
+
+    // Emit on document (only DOM events now)
+    return !document.dispatchEvent(event);
+  }
+
+  /**
+   * Log event with console grouping
+   */
+  private logEventWithGrouping(eventType: string, _detail: unknown): void {
+    // Extract category from event type (e.g., 'calendar:datechanged' → 'calendar')
+    const category = this.extractCategory(eventType);
+
+    // Only log if category is enabled
+    if (!this.logConfig[category]) {
+      return;
+    }
+
+    // Get category emoji and color (used for future console styling)
+    this.getCategoryStyle(category);
+  }
+
+  /**
+   * Extract category from event type
+   */
+  private extractCategory(eventType: string): string {
+    if (!eventType) {
+      return 'unknown';
+    }
+
+    if (eventType.includes(':')) {
+      return eventType.split(':')[0];
+    }
+
+    // Fallback: try to detect category from event name patterns
+    const lowerType = eventType.toLowerCase();
+    if (lowerType.includes('grid') || lowerType.includes('rendered')) return 'grid';
+    if (lowerType.includes('event') || lowerType.includes('sync')) return 'event';
+    if (lowerType.includes('scroll')) return 'scroll';
+    if (lowerType.includes('nav') || lowerType.includes('date')) return 'navigation';
+    if (lowerType.includes('view')) return 'view';
+
+    return 'default';
+  }
+
+  /**
+   * Get styling for different categories
+   */
+  private getCategoryStyle(category: string): { emoji: string; color: string } {
+    const styles: { [key: string]: { emoji: string; color: string } } = {
+      calendar: { emoji: '📅', color: '#2196F3' },
+      grid: { emoji: '📊', color: '#4CAF50' },
+      event: { emoji: '📌', color: '#FF9800' },
+      scroll: { emoji: '📜', color: '#9C27B0' },
+      navigation: { emoji: '🧭', color: '#F44336' },
+      view: { emoji: '👁', color: '#00BCD4' },
+      default: { emoji: '📢', color: '#607D8B' }
+    };
+
+    return styles[category] || styles.default;
+  }
+
+  /**
+   * Configure logging for specific categories
+   */
+  setLogConfig(config: { [key: string]: boolean }): void {
+    this.logConfig = { ...this.logConfig, ...config };
+  }
+
+  /**
+   * Get current log configuration
+   */
+  getLogConfig(): { [key: string]: boolean } {
+    return { ...this.logConfig };
+  }
+
+  /**
+   * Get event history
+   */
+  getEventLog(eventType?: string): IEventLogEntry[] {
+    if (eventType) {
+      return this.eventLog.filter(e => e.type === eventType);
+    }
+    return this.eventLog;
+  }
+
+  /**
+   * Enable/disable debug mode
+   */
+  setDebug(enabled: boolean): void {
+    this.debug = enabled;
+  }
+}