Add release blocklist feature

Introduce a per-request release blocklist to auto-block permanently failing releases and provide admin management. Changes include:

- Database: add BlockedRelease model (blocked_releases) to Prisma schema with unique (requestId, releaseKey) and indexes; documented in backend database docs.
- Service & utils: new blocklist.service, release-key and filter helpers for normalization and matching; processors updated to emit auto-blocks (monitor-download, organize-files, search processors, RSS).
- HTTP API: add admin endpoints GET/DELETE /api/admin/blocklist, DELETE /api/admin/blocklist/[id], and GET /api/admin/blocklist/by-request/[requestId].
- Admin UI: new /admin/blocklist page and numerous React components (toolbar, filters, table, rows, pagination, skeleton, chips, date picker) with URL-driven state hook and per-row unblock UX.
- Tests: add unit/integration tests for service, routes, utils, and updated processor tests.

The blocklist is idempotent (upsert), filters search results before ranking (interactive search shows badges only), and admin-only APIs require auth. This commit wires docs, API, DB, frontend and tests for the new feature.

prisma/schema.prisma

@@ -259,6 +259,7 @@ model Request {
   jobs            Job[]
   parentRequest   Request?          @relation("EbookParent", fields: [parentRequestId], references: [id], onDelete: SetNull)
   childRequests   Request[]         @relation("EbookParent")
+  blockedReleases BlockedRelease[]
 
   @@index([userId])
   @@index([audiobookId])
@@ -270,6 +271,42 @@ model Request {
   @@map("requests")
 }
 
+// ============================================================================
+// BLOCKED RELEASES TABLE
+// Per-request blocklist of failed releases (organize-fail or download-fail).
+// Search processors filter their candidate set against this table so future
+// searches skip releases that have already failed for the same request.
+// Documentation: documentation/backend/database.md
+// ============================================================================
+
+model BlockedRelease {
+  id                String   @id @default(uuid())
+  requestId         String   @map("request_id")
+  releaseName       String   @map("release_name") @db.Text
+  releaseKey        String   @map("release_key") @db.Text // normalized: trim + lowercase
+  releaseHash       String?  @map("release_hash") // torrentHash OR nzbId (mutually exclusive in source)
+  indexerName       String?  @map("indexer_name")
+  indexerId         Int?     @map("indexer_id")
+  source            String // 'organize_fail' | 'download_fail' | 'manual' (manual reserved for v2)
+  reason            String   @db.Text // short reason, e.g. "No audiobook files found"
+  reasonDetail      String?  @map("reason_detail") @db.Text // raw client error (SAB failMessage, NZBGet Par/Unpack)
+  downloadHistoryId String?  @map("download_history_id") // traceability to the DownloadHistory row that failed
+  jobId             String?  @map("job_id") // origin job (also drives JobEvent emission via logger)
+  createdAt         DateTime @default(now()) @map("created_at")
+
+  // Relations
+  // Cascade: hard-delete of Request wipes its blocklist rows.
+  // Soft-delete (Request.deletedAt) does NOT cascade — entries survive.
+  request Request @relation(fields: [requestId], references: [id], onDelete: Cascade)
+
+  @@unique([requestId, releaseKey]) // idempotency: one row per (request, normalized name)
+  @@index([requestId])
+  @@index([releaseKey])
+  @@index([releaseHash])
+  @@index([createdAt(sort: Desc)])
+  @@map("blocked_releases")
+}
+
 model DownloadHistory {
   id               String    @id @default(uuid())
   requestId        String    @map("request_id")