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/prisma/migrations/20260721140000_tender_bundesland_backfill/migration.sql

@@ -0,0 +1,39 @@
+-- FILTER-02 (Pitfall 1): Tender.bundesland is 100% NULL in the live DB
+-- (0/1671 rows, verified) because the Phase-10 normalizer deferred
+-- NUTS->Bundesland mapping to Phase 11. This migration:
+--   1. Adds the CREATE INDEX for bundesland (filter performance, matches
+--      schema.prisma @@index([bundesland])).
+--   2. Backfills the ~1671 pre-existing rows by deriving bundesland from
+--      the region column's NUTS-1 prefix (DE1..DEG -> the 16 Bundesländer),
+--      mirroring geo/nuts-bundesland.ts's NUTS1_BUNDESLAND map exactly.
+--
+-- Idempotent: only touches rows where bundesland IS NULL AND region IS NOT
+-- NULL — safe to run more than once, and never overwrites a value already
+-- set by the (now-fixed) normalizer for newer ingests.
+-- No user input is interpolated (T-11-05) — pure derived-field UPDATE.
+
+-- CreateIndex
+CREATE INDEX IF NOT EXISTS "Tender_bundesland_idx" ON "Tender"("bundesland");
+
+-- Backfill
+UPDATE "Tender"
+SET "bundesland" = CASE upper(left("region", 3))
+  WHEN 'DE1' THEN 'Baden-Württemberg'
+  WHEN 'DE2' THEN 'Bayern'
+  WHEN 'DE3' THEN 'Berlin'
+  WHEN 'DE4' THEN 'Brandenburg'
+  WHEN 'DE5' THEN 'Bremen'
+  WHEN 'DE6' THEN 'Hamburg'
+  WHEN 'DE7' THEN 'Hessen'
+  WHEN 'DE8' THEN 'Mecklenburg-Vorpommern'
+  WHEN 'DE9' THEN 'Niedersachsen'
+  WHEN 'DEA' THEN 'Nordrhein-Westfalen'
+  WHEN 'DEB' THEN 'Rheinland-Pfalz'
+  WHEN 'DEC' THEN 'Saarland'
+  WHEN 'DED' THEN 'Sachsen'
+  WHEN 'DEE' THEN 'Sachsen-Anhalt'
+  WHEN 'DEF' THEN 'Schleswig-Holstein'
+  WHEN 'DEG' THEN 'Thüringen'
+  ELSE NULL
+END
+WHERE "bundesland" IS NULL AND "region" IS NOT NULL;

apps/api/prisma/schema.prisma

@@ -286,6 +286,7 @@ model Tender {
   @@index([status])
   @@index([deadlineAt])
   @@index([publishedAt])
+  @@index([bundesland]) // FILTER-02: post-backfill Bundesland-Filter-Performance
   // Deliberately NO tenant column and NO tenant index — this is global data (D-03)
 }