feat: Integration Hub for external tool connectivity

- Add native config option: `new Brainy({ integrations: true })`
- OData integration for Excel Power Query and Power BI
- Google Sheets integration with Apps Script
- Server-Sent Events (SSE) for real-time streaming
- Webhooks for push notifications
- Zero-config with sensible defaults
- Full tree-shaking when disabled

src/integrations/core/index.ts

@@ -0,0 +1,64 @@
+/**
+ * Integration Hub - Core Infrastructure
+ *
+ * Shared foundation for all integrations:
+ * - EventBus: Real-time change notifications
+ * - TabularExporter: Entity to rows/columns conversion
+ * - IntegrationBase: Base class for integrations
+ * - IntegrationHub: Zero-config integration manager
+ */
+
+// Event system
+export { EventBus } from './EventBus.js'
+
+// Tabular export
+export { TabularExporter } from './TabularExporter.js'
+
+// Base class
+export {
+  IntegrationBase,
+  type HTTPIntegration,
+  type StreamingIntegration
+} from './IntegrationBase.js'
+
+// Integration loader
+export {
+  IntegrationLoader,
+  createIntegrationLoader,
+  detectEnvironment,
+  INTEGRATION_CATALOG,
+  type IntegrationType,
+  type RuntimeEnvironment,
+  type IntegrationInfo,
+  type IntegrationLoaderConfig
+} from './IntegrationLoader.js'
+
+// Zero-config hub
+export {
+  IntegrationHub,
+  createIntegrationHub,
+  type IntegrationHubConfig,
+  type IntegrationRequest,
+  type IntegrationResponse
+} from './IntegrationHub.js'
+
+// Types
+export type {
+  // Events
+  BrainyEvent,
+  EventFilter,
+  EventHandler,
+  EventSubscription,
+  // Tabular
+  TabularRow,
+  RelationTabularRow,
+  TabularExporterConfig,
+  // Config
+  IntegrationConfig,
+  IntegrationHealthStatus,
+  // OData
+  ODataQueryOptions,
+  // Webhooks
+  WebhookRegistration,
+  WebhookDeliveryResult
+} from './types.js'