feat: LibraryItem.requestId nullable (scanned haves need no request) + test cleanup

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

web/prisma/migrations/20260711145610_library_item_optional_request/migration.sql

@@ -0,0 +1,2 @@
+-- AlterTable
+ALTER TABLE "LibraryItem" ALTER COLUMN "requestId" DROP NOT NULL;

web/prisma/schema.prisma

@@ -72,8 +72,8 @@ model Candidate {
 
 model LibraryItem {
   id           String   @id @default(cuid())
-  request      Request  @relation(fields: [requestId], references: [id], onDelete: Cascade)
-  requestId    String   @unique
+  request      Request? @relation(fields: [requestId], references: [id], onDelete: Cascade)
+  requestId    String?  @unique
   artist       String
   album        String
   path         String

web/src/test/setup.ts

@@ -12,6 +12,7 @@ beforeEach(async () => {
   // Job cascades from Request; Request.monitoredReleaseId is SetNull. Delete children first.
   await prisma.job.deleteMany();
   await prisma.request.deleteMany();
+  await prisma.libraryItem.deleteMany();
   await prisma.monitoredRelease.deleteMany();
   await prisma.watchedArtist.deleteMany();
   await prisma.config.deleteMany();