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/fr.ts

@@ -138,6 +138,9 @@ const fr = {
   "libraries.imminent": "Imminent",
   "libraries.nextMetadataRefresh": "Prochain rafraîchissement méta. : {{time}}",
   "libraries.nextMetadataRefreshShort": "Méta. : {{time}}",
+  "libraries.scanLabel": "Scan : {{mode}}",
+  "libraries.watcherLabel": "Surveillance fichiers",
+  "libraries.metaRefreshLabel": "Rafraîch. méta. : {{mode}}",
   "libraries.index": "Indexer",
   "libraries.fullIndex": "Complet",
   "libraries.batchMetadata": "Métadonnées en lot",
@@ -155,14 +158,22 @@ const fr = {
   "librarySeries.noBooksInSeries": "Aucun livre dans cette série",
 
   // Library actions
-  "libraryActions.autoScan": "Scan auto",
-  "libraryActions.fileWatch": "Surveillance fichiers ⚡",
-  "libraryActions.schedule": "📅 Planification",
+  "libraryActions.settingsTitle": "Paramètres de la bibliothèque",
+  "libraryActions.sectionIndexation": "Indexation",
+  "libraryActions.sectionMetadata": "Métadonnées",
+  "libraryActions.autoScan": "Scan planifié",
+  "libraryActions.autoScanDesc": "Scanner automatiquement les fichiers nouveaux et modifiés",
+  "libraryActions.fileWatch": "Surveillance en temps réel",
+  "libraryActions.fileWatchDesc": "Détecter les changements de fichiers instantanément",
+  "libraryActions.schedule": "Fréquence",
   "libraryActions.provider": "Fournisseur",
-  "libraryActions.fallback": "Secours",
+  "libraryActions.providerDesc": "Source utilisée pour récupérer les métadonnées des séries",
+  "libraryActions.fallback": "Fournisseur de secours",
+  "libraryActions.fallbackDesc": "Utilisé quand le fournisseur principal ne retourne aucun résultat",
   "libraryActions.default": "Par défaut",
   "libraryActions.none": "Aucun",
-  "libraryActions.metadataRefreshSchedule": "Rafraîchir méta.",
+  "libraryActions.metadataRefreshSchedule": "Rafraîchissement auto",
+  "libraryActions.metadataRefreshDesc": "Re-télécharger périodiquement les métadonnées existantes",
   "libraryActions.saving": "Enregistrement...",
 
   // Library sub-page header