feat(11-02): normalizer derives bundesland + backfill migration for existing rows

Replace the Phase-10-deferred `bundesland = null` assignment with
bundeslandFromRegion(region) so new ingests are Bundesland-filterable
immediately. Add @@index([bundesland]) for filter performance. New
handwritten migration 20260721140000_tender_bundesland_backfill backfills
the ~1671 pre-existing rows (idempotent UPDATE, only where bundesland IS
NULL AND region IS NOT NULL) — applied locally via
`docker exec tessera-ctl-db-1 psql`, resolved as applied in
_prisma_migrations, and prisma generate re-run.

Verified on the local dev DB: 933/1671 rows now have bundesland set
across all 16 Länder (738 remain NULL where region itself is NULL).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/api/src/tenders/tender-normalizer.service.ts

@@ -1,5 +1,6 @@
 import { Injectable } from '@nestjs/common';
 import { createHash } from 'crypto';
+import { bundeslandFromRegion } from './geo/nuts-bundesland';
 import type { NormalizedTenderFields, RawTenderRecord } from './tender.types';
 
 /**
@@ -33,9 +34,11 @@ export class TenderNormalizerService {
     const cpvCodes = extractCpvCodes(ocdsTender);
     const region = textValue(ocdsBuyer?.address?.region);
     const plz = textValue(ocdsBuyer?.address?.postalCode);
-    // NUTS->Bundesland name mapping deferred to Phase 11 (filter UI) — not
-    // required for this phase's ingestion core.
-    const bundesland: string | null = null;
+    // Phase 11 (FILTER-02, Pitfall 1): derive bundesland from region's
+    // NUTS-1 prefix so new ingests are filterable immediately — the
+    // ~1671 pre-existing rows are backfilled by a one-time migration
+    // (20260721140000_tender_bundesland_backfill).
+    const bundesland = bundeslandFromRegion(region);
 
     const deadlineAt =
       extractEformsDeadline(eformsRoot) ??