feat: redesign libraries page UI with fan thumbnails and modal settings

- Replace thumbnail mosaic with fan/arc layout using series covers as background
- Move library settings from dropdown to full-page portal modal with sections
- Move FolderPicker modal to portal for proper z-index stacking
- Add descriptions to each setting for better clarity
- Move delete button to card header, compact config tags
- Add i18n keys for new labels and descriptions (en/fr)

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

apps/backoffice/lib/i18n/en.ts

@@ -140,6 +140,9 @@ const en: Record<TranslationKey, string> = {
   "libraries.imminent": "Imminent",
   "libraries.nextMetadataRefresh": "Next metadata refresh: {{time}}",
   "libraries.nextMetadataRefreshShort": "Meta.: {{time}}",
+  "libraries.scanLabel": "Scan: {{mode}}",
+  "libraries.watcherLabel": "File watch",
+  "libraries.metaRefreshLabel": "Meta refresh: {{mode}}",
   "libraries.index": "Index",
   "libraries.fullIndex": "Full",
   "libraries.batchMetadata": "Batch metadata",
@@ -157,14 +160,22 @@ const en: Record<TranslationKey, string> = {
   "librarySeries.noBooksInSeries": "No books in this series",
 
   // Library actions
-  "libraryActions.autoScan": "Auto scan",
-  "libraryActions.fileWatch": "File watch ⚡",
-  "libraryActions.schedule": "📅 Schedule",
+  "libraryActions.settingsTitle": "Library settings",
+  "libraryActions.sectionIndexation": "Indexation",
+  "libraryActions.sectionMetadata": "Metadata",
+  "libraryActions.autoScan": "Scheduled scan",
+  "libraryActions.autoScanDesc": "Automatically scan for new and modified files",
+  "libraryActions.fileWatch": "Real-time file watch",
+  "libraryActions.fileWatchDesc": "Detect file changes instantly via filesystem events",
+  "libraryActions.schedule": "Frequency",
   "libraryActions.provider": "Provider",
-  "libraryActions.fallback": "Fallback",
+  "libraryActions.providerDesc": "Source used to fetch series and volume metadata",
+  "libraryActions.fallback": "Fallback provider",
+  "libraryActions.fallbackDesc": "Used when the primary provider returns no results",
   "libraryActions.default": "Default",
   "libraryActions.none": "None",
-  "libraryActions.metadataRefreshSchedule": "Refresh meta.",
+  "libraryActions.metadataRefreshSchedule": "Auto-refresh",
+  "libraryActions.metadataRefreshDesc": "Periodically re-fetch metadata for existing series",
   "libraryActions.saving": "Saving...",
 
   // Library sub-page header