feat: add Prowlarr integration for manual release search

Add Prowlarr indexer integration (step 1: config + manual search).
Allows searching for comics/ebooks releases on Prowlarr indexers
directly from the series detail page, with download links and
per-volume search for missing books.

- Backend: new prowlarr module with search and test endpoints
- Migration: add prowlarr settings (url, api_key, categories)
- Settings UI: Prowlarr config card with test connection button
- ProwlarrSearchModal: auto-search on open, missing volumes shortcuts
- Fix series.readCount i18n plural parameter on series pages

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/backoffice/lib/i18n/en.ts

@@ -458,6 +458,40 @@ const en: Record<TranslationKey, string> = {
   "settings.newTargetPlaceholder": "New target status (e.g. hiatus)",
   "settings.createTargetStatus": "Create status",
 
+  // Settings - Prowlarr
+  "settings.prowlarr": "Prowlarr",
+  "settings.prowlarrDesc": "Configure Prowlarr to search for releases on indexers (torrents/usenet). Only manual search is available for now.",
+  "settings.prowlarrUrl": "Prowlarr URL",
+  "settings.prowlarrUrlPlaceholder": "http://localhost:9696",
+  "settings.prowlarrApiKey": "API Key",
+  "settings.prowlarrApiKeyPlaceholder": "Prowlarr API key",
+  "settings.prowlarrCategories": "Categories",
+  "settings.prowlarrCategoriesHelp": "Comma-separated Newznab category IDs (7030 = Comics, 7020 = Ebooks)",
+  "settings.testConnection": "Test connection",
+  "settings.testing": "Testing...",
+  "settings.testSuccess": "Connection successful",
+  "settings.testFailed": "Connection failed",
+
+  // Prowlarr search modal
+  "prowlarr.searchButton": "Prowlarr",
+  "prowlarr.modalTitle": "Prowlarr Search",
+  "prowlarr.searchSeries": "Search series",
+  "prowlarr.searchVolume": "Search",
+  "prowlarr.searching": "Searching...",
+  "prowlarr.noResults": "No results found",
+  "prowlarr.resultCount": "{{count}} result{{plural}}",
+  "prowlarr.missingVolumes": "Missing volumes",
+  "prowlarr.columnTitle": "Title",
+  "prowlarr.columnIndexer": "Indexer",
+  "prowlarr.columnSize": "Size",
+  "prowlarr.columnSeeders": "Seeds",
+  "prowlarr.columnLeechers": "Peers",
+  "prowlarr.columnProtocol": "Protocol",
+  "prowlarr.searchError": "Search failed",
+  "prowlarr.notConfigured": "Prowlarr is not configured",
+  "prowlarr.download": "Download",
+  "prowlarr.info": "Info",
+
   // Settings - Language
   "settings.language": "Language",
   "settings.languageDesc": "Choose the interface language",