refactor: centralize modals, fix cross-chat ID collisions, address review feedback

- Extract ChatAvatar component replacing 3 inline avatar implementations
- Add shared formatRelativeDate helper (label/compact modes)
- Add Button size="lg" variant with disabled styles
- Vertically center Modal on all breakpoints, not just desktop
- RestoreSessionModal: remove description banner, only chat list scrolls,
  fixed footer with action buttons
- Fix message ID collisions across chats by including filename in hash
- Fix Toast timer not restarting when message changes while visible
- Gate reselect flow: only upgrade persisted entry when validation passes
- Add persistence_restore_failed i18n key across all 10 locales
- Remove unused isFileSystemAccessSupported import and function

Author: rodrigogs

messages/de.json

@@ -261,6 +261,7 @@
   "persistence_or_browse": "oder klicken Sie unten zum Durchsuchen",
   "persistence_browse_files": "Dateien durchsuchen",
   "persistence_save_failed": "Fehler beim Speichern der Unterhaltung",
+  "persistence_restore_failed": "Fehler beim Wiederherstellen der Unterhaltung",
   "persistence_remove_failed": "Fehler beim Entfernen der Unterhaltung",
   "close_notification": "Benachrichtigung schließen"
 }

messages/en.json

@@ -262,6 +262,7 @@
   "persistence_or_browse": "or click below to browse",
   "persistence_browse_files": "Browse Files",
   "persistence_save_failed": "Failed to save conversation",
+  "persistence_restore_failed": "Failed to restore conversation",
   "persistence_remove_failed": "Failed to remove conversation",
   "close_notification": "Close notification"
 }

messages/es.json

@@ -261,6 +261,7 @@
   "persistence_or_browse": "o haz clic abajo para buscar",
   "persistence_browse_files": "Buscar Archivos",
   "persistence_save_failed": "Error al guardar la conversación",
+  "persistence_restore_failed": "Error al restaurar la conversación",
   "persistence_remove_failed": "Error al eliminar la conversación",
   "close_notification": "Cerrar notificación"
 }

messages/fr.json

@@ -261,6 +261,7 @@
   "persistence_or_browse": "ou cliquez ci-dessous pour parcourir",
   "persistence_browse_files": "Parcourir les fichiers",
   "persistence_save_failed": "Échec de l'enregistrement de la conversation",
+  "persistence_restore_failed": "Échec de la restauration de la conversation",
   "persistence_remove_failed": "Échec de la suppression de la conversation",
   "close_notification": "Fermer la notification"
 }

messages/it.json

@@ -261,6 +261,7 @@
   "persistence_or_browse": "o clicca sotto per sfogliare",
   "persistence_browse_files": "Sfoglia file",
   "persistence_save_failed": "Impossibile salvare la conversazione",
+  "persistence_restore_failed": "Impossibile ripristinare la conversazione",
   "persistence_remove_failed": "Impossibile rimuovere la conversazione",
   "close_notification": "Chiudi notifica"
 }

messages/ja.json

@@ -261,6 +261,7 @@
   "persistence_or_browse": "または下をクリックして参照",
   "persistence_browse_files": "ファイルを参照",
   "persistence_save_failed": "会話の保存に失敗しました",
+  "persistence_restore_failed": "会話の復元に失敗しました",
   "persistence_remove_failed": "会話の削除に失敗しました",
   "close_notification": "通知を閉じる"
 }

messages/nl.json

@@ -261,6 +261,7 @@
   "persistence_or_browse": "of klik hieronder om te bladeren",
   "persistence_browse_files": "Bestanden bladeren",
   "persistence_save_failed": "Gesprek opslaan mislukt",
+  "persistence_restore_failed": "Gesprek herstellen mislukt",
   "persistence_remove_failed": "Gesprek verwijderen mislukt",
   "close_notification": "Melding sluiten"
 }

messages/pt.json

@@ -261,6 +261,7 @@
   "persistence_or_browse": "ou clique abaixo para procurar",
   "persistence_browse_files": "Procurar Arquivos",
   "persistence_save_failed": "Falha ao salvar conversa",
+  "persistence_restore_failed": "Falha ao restaurar conversa",
   "persistence_remove_failed": "Falha ao remover conversa",
   "close_notification": "Fechar notificação"
 }

messages/ru.json

@@ -261,6 +261,7 @@
   "persistence_or_browse": "или нажмите ниже для поиска",
   "persistence_browse_files": "Обзор файлов",
   "persistence_save_failed": "Не удалось сохранить разговор",
+  "persistence_restore_failed": "Не удалось восстановить разговор",
   "persistence_remove_failed": "Не удалось удалить разговор",
   "close_notification": "Закрыть уведомление"
 }

messages/zh.json

@@ -261,6 +261,7 @@
   "persistence_or_browse": "或点击下方浏览",
   "persistence_browse_files": "浏览文件",
   "persistence_save_failed": "保存对话失败",
+  "persistence_restore_failed": "恢复对话失败",
   "persistence_remove_failed": "删除对话失败",
   "close_notification": "关闭通知"
 }