feat: add server-side ETL pipeline, revert client to NocoDB reads

ETL Pipeline (server):
- POST /api/etl/sync?mode=full|incremental — fetches ERP, aggregates, writes NocoDB
- nocodbClient.ts: table discovery, paginated delete/insert
- etlSync.ts: orchestrates fetch → aggregate → upsert
- museumMapping.ts moved from client to server
- Auth via ETL_SECRET bearer token

Client:
- dataService.ts reverts to reading NocoDB DailySales table
- Paginated fetch via fetchNocoDBTable (handles >1000 rows)
- Suspicious data check: prefers cache if NocoDB returns <10 rows
- Deleted erpService.ts and client-side museumMapping.ts

First full sync: 391K transactions → 5,760 daily records in 108s.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/src/routes/etl.ts

@@ -0,0 +1,34 @@
+import { Router, Request, Response } from 'express';
+import { etl } from '../config';
+import { runSync } from '../services/etlSync';
+
+const router = Router();
+
+// POST /api/etl/sync?mode=full|incremental
+router.post('/sync', async (req: Request, res: Response) => {
+  // Auth check
+  const auth = req.headers.authorization;
+  if (etl.secret && auth !== `Bearer ${etl.secret}`) {
+    res.status(401).json({ error: 'Unauthorized' });
+    return;
+  }
+
+  const mode = (req.query.mode as string) === 'full' ? 'full' : 'incremental';
+
+  try {
+    console.log(`\nETL sync started (${mode})...`);
+    const result = await runSync(mode);
+    console.log(`ETL sync complete: ${result.transactionsFetched} transactions → ${result.recordsWritten} records in ${result.duration}`);
+    res.json(result);
+  } catch (err) {
+    console.error('ETL sync failed:', (err as Error).message);
+    res.status(500).json({ error: 'ETL sync failed', details: (err as Error).message });
+  }
+});
+
+// GET /api/etl/status
+router.get('/status', (_req: Request, res: Response) => {
+  res.json({ configured: !!etl.secret });
+});
+
+export default router;