Add skip-unreleased auto-search feature

Introduce an indexer-wide option to skip automatic searches for books with future release dates (config key: `indexer.skip_unreleased`, default ON). Adds a GET/PUT admin API for indexer options, a UI toggle on the Indexers settings tab (persisted on save), and persistence of a request-level releaseDate in the Prisma schema.

Adds a new request status `awaiting_release` and wires it through constants, UI components (StatusBadge, RequestCard, RecentRequestsTable, Audiobook card/modal, RequestActions), API request flows (bookdate swipe, request creation, manual search, request PATCHs, request listing groups), and services. Implements a pure release-date utility (isUnreleased / shouldSkipAutoSearch) and updates background processors: monitor-rss-feeds (skip matches but do not mutate status), retry-missing-torrents (drives bidirectional transitions between awaiting_search and awaiting_release and queues searches when appropriate), and request-creator/bookdate swipe (gate initial auto-search). Adds tests for the swipe gate and other related test updates. Logs transitions and gate decisions for observability.

documentation/backend/services/jobs.md

@@ -48,6 +48,7 @@ Manages background job queue using Bull (Redis-backed) for async tasks: searchin
 **search_indexers:**
 - No torrents found → 'awaiting_search' status (not failed)
 - Allows automatic retry via scheduled job
+- Upstream release-date gate: 4 enqueue sites (`request-creator.service`, `retry-missing-torrents.processor`, `monitor-rss-feeds.processor`, `bookdate/swipe/route`) check `shouldSkipAutoSearch` against `indexer.skip_unreleased`; gated requests are created/kept in `awaiting_release` and `addSearchJob` is not called. Manual search bypasses the gate.
 
 **organize_files:**
 - No audiobook files found → 'awaiting_import' status