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/types.ts

@@ -0,0 +1,27 @@
+export interface ERPProduct {
+  ProductDescription: string;
+  SiteDescription: string | null;
+  UnitQuantity: number;
+  PeopleCount: number;
+  TaxAmount: number;
+  TotalPrice: number;
+}
+
+export interface ERPSaleRecord {
+  SaleId: number;
+  TransactionDate: string;
+  CustIdentification: string;
+  OperatingAreaName: string;
+  Payments: Array<{ PaymentMethodDescription: string }>;
+  Products: ERPProduct[];
+}
+
+export interface AggregatedRecord {
+  Date: string;
+  MuseumName: string;
+  Channel: string;
+  Visits: number;
+  Tickets: number;
+  GrossRevenue: number;
+  NetRevenue: number;
+}