perf(learn): a conversation deleted goes at once, with an Undo

Deleting a kept conversation asked first and then waited while its
turns were blanked and deleted. It now goes as a card or a note does:
ConversationDeletions, a DelayedDeletions opened with the person's
data, takes it off the history at once (the list leaves out what is
pending), offers Undo for a moment on the sheet (hasSnackBars), and
blanks and deletes it once that is over; a deletion that fails shows
the conversation again, as every DelayedDeletions does. The question
before deleting goes, as Undo replaces it.

Whats-New: A conversation with an assistant is deleted at once, and Undo brings it back.
Whats-New-De: Eine Unterhaltung mit einem Assistenten wird sofort gelöscht, und „Rückgängig“ holt sie zurück.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/learn/halkyon_learn_flutter/lib/l10n/app_localizations.dart

@@ -10497,17 +10497,11 @@ abstract class AppLocalizations {
   /// **'Delete conversation'**
   String get assistantHistoryDelete;
 
-  /// No description provided for @assistantHistoryDeleteMessage.
+  /// No description provided for @assistantHistoryDeleted.
   ///
   /// In en, this message translates to:
-  /// **'“{title}” goes from all your devices.'**
-  String assistantHistoryDeleteMessage(String title);
-
-  /// No description provided for @assistantHistoryDeleteConfirm.
-  ///
-  /// In en, this message translates to:
-  /// **'Delete'**
-  String get assistantHistoryDeleteConfirm;
+  /// **'Conversation deleted'**
+  String get assistantHistoryDeleted;
 
   /// No description provided for @assistantGone.
   ///