feat(13-01): add TenderSource model + Tender.fingerprint, backfill 2851 rows

Additive schema change (SCHEMA-03/D-03/D-04): new model TenderSource
(1:n Tender, @@unique[sourcePortal, sourceNoticeId], onDelete Cascade)
and a nullable Tender.fingerprint column + index. dedupKey stays
unchanged as the SCHEMA-02 upsert target.

Migration 20260723120000_add_tender_source applies in strict order
(Pitfall 5): table+column create, then one TenderSource row per
pre-existing Tender via SQL INSERT/SELECT, then the unique constraint.
Applied locally against the tessera dev DB (container IP, no host
port) — verified via psql: TenderSource count == Tender count == 2851.

backfill-tender-source.ts is a one-time script that computes
Tender.fingerprint via the Task-1 tenderFingerprint() function
(Decimal->number conversion for estimatedValue, T-13-01-03) — run via
the compiled dist/ output (source uses standard extensionless TS
imports for tsc compatibility). Confirmed: 2851/2851 rows backfilled,
idempotent re-run verified.

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

apps/api/prisma/schema.prisma

@@ -281,6 +281,10 @@ model Tender {
   sourceUrl      String?
   contentHash    String // SCHEMA-02 change detection
   rawPayload     Json? // debugging / re-normalization
+  // SCHEMA-03 (D-04) — Fuzzy-Dedup lookup key, additive + nullable. Backfilled
+  // for pre-existing rows by backfill-tender-source.ts (Plan 13-01 Task 2).
+  // dedupKey above stays the SCHEMA-02 upsert target — NOT replaced here.
+  fingerprint    String?
   publishedAt    DateTime
   createdAt      DateTime  @default(now())
   updatedAt      DateTime  @updatedAt
@@ -290,9 +294,30 @@ model Tender {
   @@index([publishedAt])
   @@index([bundesland]) // FILTER-02: post-backfill Bundesland-Filter-Performance
   @@index([cpvDivisions], type: Gin) // FILTER-03: post-backfill CPV-Divisions-Filter-Performance (hasSome)
+  @@index([fingerprint]) // SCHEMA-03: dedup resolver fingerprint-tier lookup
   // Deliberately NO tenant column and NO tenant index — this is global data (D-03)
   triage  TenderTriage[]
   matches TenderMatch[]
+  sources TenderSource[] // SCHEMA-03/D-03 — all source portals this tender was seen on
+}
+
+// SCHEMA-03 (D-03) — Quell-Ebene einer Ausschreibung. 1:n zu Tender: ein
+// Tender ist EIN Trefferlisten-Eintrag; mehrere TenderSource-Zeilen sind die
+// Liste der Quell-Portale/Links, über die er gefunden wurde (Cross-Source
+// Dedup, "ein Eintrag + Liste ALLER Quell-Links", nicht "Primärquelle
+// gewinnt"). Backfilled 1:1 for pre-existing DÖE tenders (D-05).
+model TenderSource {
+  id             String   @id @default(uuid())
+  tenderId       String
+  sourcePortal   String // 'doe-opendata' | 'tender24' | 'lhs-vpbw' | 'vergabe.landbw' | 'cosinex-dtvp'
+  sourceNoticeId String
+  ocid           String?
+  sourceUrl      String?
+  createdAt      DateTime @default(now())
+  tender         Tender   @relation(fields: [tenderId], references: [id], onDelete: Cascade)
+
+  @@unique([sourcePortal, sourceNoticeId]) // eine Quell-Notiz gehört zu genau einem Tender
+  @@index([tenderId])
 }
 
 // UI-03/04 — per-user Triage-Zustand pro Tender (gelesen/ungelesen, Favorit).