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

integrations/google-sheets/README.md

@@ -0,0 +1,142 @@
+# Brainy Google Sheets Add-on
+
+Two-way sync between Brainy and Google Sheets.
+
+## Quick Setup
+
+1. Open your Google Sheet
+2. Go to **Extensions → Apps Script**
+3. Delete any existing code
+4. Copy and paste `Code.gs` into the editor
+5. Create a new HTML file called `Sidebar.html` and paste the content
+6. Go to **Project Settings** (gear icon) → **Script properties**
+7. Add property: `BRAINY_URL` = your Brainy server URL (e.g., `http://localhost:3000`)
+8. Save and refresh your spreadsheet
+
+## Custom Functions
+
+Use these directly in cells:
+
+### `=BRAINY_QUERY(query, limit)`
+Query entities using semantic search or type filter.
+
+```
+=BRAINY_QUERY("machine learning", 10)
+=BRAINY_QUERY("type:person", 100)
+```
+
+### `=BRAINY_GET(id)`
+Get a single entity by ID.
+
+```
+=BRAINY_GET("entity-uuid-here")
+```
+
+### `=BRAINY_SIMILAR(text, limit)`
+Find semantically similar entities.
+
+```
+=BRAINY_SIMILAR("artificial intelligence research", 5)
+```
+
+### `=BRAINY_RELATIONS(entityId, direction)`
+Get relationships for an entity.
+
+```
+=BRAINY_RELATIONS("entity-id", "from")
+=BRAINY_RELATIONS("entity-id", "to")
+=BRAINY_RELATIONS("entity-id", "both")
+```
+
+### `=BRAINY_TYPES()`
+List all available entity types.
+
+### `=BRAINY_RELATION_TYPES()`
+List all available relationship types.
+
+## Sidebar
+
+Open via **Brainy → Open Sidebar** menu:
+
+- **Search**: Query entities and insert results into the sheet
+- **Add**: Create new entities with a form
+- **Sync**: Sync selected range to Brainy (add or update)
+
+## Authentication
+
+If your Brainy server requires authentication:
+
+1. Go to **Project Settings → Script properties**
+2. Add property: `BRAINY_API_KEY` = your API key
+
+## Real-Time Sync
+
+For real-time updates, enable SSE in your Brainy server:
+
+```javascript
+brain.augmentations.register(new SSEIntegration())
+```
+
+The sidebar will automatically show changes as they happen.
+
+## Troubleshooting
+
+### "Brainy URL not configured"
+Add the `BRAINY_URL` script property in Apps Script settings.
+
+### "Connection failed"
+- Check that your Brainy server is running
+- Ensure the URL is correct (include port if needed)
+- For local development, use ngrok or similar to expose localhost
+
+### Custom functions not appearing
+- Refresh the spreadsheet
+- Wait a few seconds (Apps Script can be slow to register)
+- Check the Apps Script execution log for errors
+
+## Server Setup
+
+The simplest way to enable all integrations:
+
+```javascript
+import { Brainy } from '@soulcraft/brainy'
+
+const brain = new Brainy({ integrations: true })
+await brain.init()
+
+console.log(brain.hub.endpoints)
+// { odata: '/odata', sheets: '/sheets', sse: '/events', webhooks: '/webhooks' }
+```
+
+With Express:
+
+```javascript
+import express from 'express'
+import { Brainy } from '@soulcraft/brainy'
+
+const app = express()
+const brain = new Brainy({ integrations: true })
+await brain.init()
+
+// Route all integration requests
+app.use(express.json())
+app.all(['/odata/*', '/sheets/*', '/events/*'], async (req, res) => {
+  const response = await brain.hub.handleRequest({
+    method: req.method,
+    path: req.path,
+    query: req.query,
+    headers: req.headers,
+    body: req.body
+  })
+
+  if (response.isSSE) {
+    // Handle SSE stream
+    res.setHeader('Content-Type', 'text/event-stream')
+    // ... streaming logic
+  } else {
+    res.status(response.status).set(response.headers).json(response.body)
+  }
+})
+
+app.listen(3000)
+```