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/config.ts

@@ -23,3 +23,13 @@ export const erp = {
   username: process.env.ERP_USERNAME || '',
   password: process.env.ERP_PASSWORD || '',
 };
+
+export const nocodb = {
+  url: process.env.NOCODB_URL || '',
+  token: process.env.NOCODB_TOKEN || '',
+  baseId: process.env.NOCODB_BASE_ID || '',
+};
+
+export const etl = {
+  secret: process.env.ETL_SECRET || '',
+};