Suppress mentions on embed-only wipe posts

Only pass AllowedMentions.All when ping content is present; use
AllowedMentions.None for embed-only posts so incidental mention-like
text in the localized embed cannot ping users or roles.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: HandyS11

src/RustPlusBot.Features.Wipes/Posting/DiscordWipeChannelPoster.cs

@@ -26,11 +26,14 @@ public async Task PostAsync(ulong channelId, string? content, Embed embed, Cance
                 return;
             }
 
+            // Only permit mentions when we are deliberately pinging (content carries the @everyone).
+            // For an embed-only post, suppress all mentions so incidental mention-like text in the
+            // localized embed can never ping a user or role.
             await channel.SendMessageAsync(
                     content,
                     embed: embed,
                     options: options,
-                    allowedMentions: AllowedMentions.All)
+                    allowedMentions: content is null ? AllowedMentions.None : AllowedMentions.All)
                 .ConfigureAwait(false);
         }
         catch (OperationCanceledException)