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/index.ts

@@ -0,0 +1,138 @@
+/**
+ * Brainy Integration Hub
+ *
+ * Connect Brainy to external tools with zero configuration:
+ * - Google Sheets (two-way sync)
+ * - Excel / Power BI / Tableau (OData 4.0)
+ * - Real-time dashboards (SSE streaming)
+ * - External webhooks (push notifications)
+ *
+ * @example Enable integrations (v7.4.0 - recommended)
+ * ```typescript
+ * import { Brainy } from '@soulcraft/brainy'
+ *
+ * const brain = new Brainy({ integrations: true })
+ * await brain.init()
+ *
+ * // Access the hub
+ * console.log(brain.hub.endpoints)
+ * // { odata: '/odata', sheets: '/sheets', sse: '/events', webhooks: '/webhooks' }
+ *
+ * // Handle requests (Express, Hono, etc.)
+ * app.all('/odata/*', async (req, res) => {
+ *   const response = await brain.hub.handleRequest(req)
+ *   res.status(response.status).json(response.body)
+ * })
+ * ```
+ */
+
+// ============================================================================
+// Integration Hub (used internally by brain.hub)
+// ============================================================================
+
+export {
+  IntegrationHub,
+  createIntegrationHub,
+  type IntegrationHubConfig,
+  type IntegrationRequest,
+  type IntegrationResponse
+} from './core/IntegrationHub.js'
+
+// ============================================================================
+// Core Infrastructure
+// ============================================================================
+
+export {
+  // Event system for real-time updates
+  EventBus,
+  // Entity → rows/columns conversion
+  TabularExporter,
+  // Base class for custom integrations
+  IntegrationBase,
+  // Lazy-loading manager
+  IntegrationLoader,
+  createIntegrationLoader,
+  // Environment detection
+  detectEnvironment,
+  // Integration catalog
+  INTEGRATION_CATALOG
+} from './core/index.js'
+
+// Types
+export type {
+  HTTPIntegration,
+  StreamingIntegration,
+  IntegrationType,
+  RuntimeEnvironment,
+  IntegrationInfo,
+  IntegrationLoaderConfig
+} from './core/index.js'
+
+export type {
+  BrainyEvent,
+  EventFilter,
+  EventHandler,
+  EventSubscription,
+  TabularRow,
+  RelationTabularRow,
+  TabularExporterConfig,
+  IntegrationConfig,
+  IntegrationHealthStatus,
+  ODataQueryOptions,
+  WebhookRegistration,
+  WebhookDeliveryResult
+} from './core/index.js'
+
+// ============================================================================
+// Individual Integrations
+// ============================================================================
+
+/**
+ * OData 4.0 Integration
+ *
+ * Connect Excel Power Query, Power BI, Tableau, and any OData client.
+ */
+export { ODataIntegration, type ODataConfig } from './odata/index.js'
+
+/**
+ * Google Sheets Integration
+ *
+ * Two-way sync between Brainy and Google Sheets via Apps Script.
+ */
+export { GoogleSheetsIntegration, type GoogleSheetsConfig } from './sheets/index.js'
+
+/**
+ * SSE Streaming Integration
+ *
+ * Real-time event streaming via Server-Sent Events.
+ */
+export { SSEIntegration, type SSEConfig } from './sse/index.js'
+
+/**
+ * Webhook Integration
+ *
+ * Push events to external URLs with retry and signing.
+ */
+export { WebhookIntegration, type WebhookConfig } from './webhooks/index.js'
+
+// ============================================================================
+// OData Utilities (for advanced use)
+// ============================================================================
+
+export {
+  parseODataQuery,
+  parseFilter,
+  parseOrderBy,
+  parseSelect,
+  odataToFindParams,
+  applyFilter,
+  applySelect,
+  applyOrderBy,
+  applyPagination
+} from './odata/ODataQueryParser.js'
+
+export {
+  generateEdmx,
+  generateMetadataJson,
+  generateServiceDocument
+} from './odata/EdmxGenerator.js'