feat(11-06): TenderSavedSearch model + CRUD service (FILTER-06)

GREEN phase — adds TenderSavedSearch (userId+tenantId scoped, filters
Json, @@unique([userId,name])), the migration (applied to local dev DB),
and TenderSavedSearchService following the FavoritesService/
TenderTriageService pattern: manual where:{userId} scoping (no
forTenant()/RLS), ownership check before update/remove, P2002 unique
conflicts translated to ConflictException.

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

apps/api/prisma/migrations/20260721170000_add_tender_saved_search/migration.sql

@@ -0,0 +1,25 @@
+-- CreateTable
+-- FILTER-06 (D-08/D-11) — per-user Suchprofil (benannte Filterkombination).
+-- Scoping-Muster wie FavoriteLink/TenderTriage (T-08-06, Pitfall 4):
+-- userId-Scoping im Service, KEIN forTenant()/RLS. tenantId wird
+-- zusätzlich mitgeführt (spätere Tenant-Isolation), ist aber nicht das
+-- Scoping-Feld. KEIN Tender-FK (Pitfall 6) — filters speichert nur
+-- Kriterien, nicht Tender-Ids, daher unkritisch bei der Retention.
+CREATE TABLE IF NOT EXISTS "TenderSavedSearch" (
+    "id" TEXT NOT NULL,
+    "userId" TEXT NOT NULL,
+    "tenantId" TEXT NOT NULL,
+    "name" TEXT NOT NULL,
+    "filters" JSONB NOT NULL,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updatedAt" TIMESTAMP(3) NOT NULL,
+
+    CONSTRAINT "TenderSavedSearch_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+-- Verhindert zwei Profile gleichen Namens pro Nutzer (T-11-14).
+CREATE UNIQUE INDEX IF NOT EXISTS "TenderSavedSearch_userId_name_key" ON "TenderSavedSearch"("userId", "name");
+
+-- CreateIndex
+CREATE INDEX IF NOT EXISTS "TenderSavedSearch_userId_idx" ON "TenderSavedSearch"("userId");