feat(feedback): snapshot the sender's language and connector bot at submit

Store the sender's interface language (lang) and, for a message that arrived
through an external connector (Telegram), the bot language (channel_lang) on the
feedback row at submit time, so the operator console shows the state as it was
rather than the account's current settings (same snapshot discipline as a
suspension reason). Added additively in migration 00005. The console detail reads
these columns instead of loading the account live.

backend/internal/feedback/service.go

@@ -111,7 +111,15 @@ func (svc *Service) Submit(ctx context.Context, accountID uuid.UUID, body string
 	} else {
 		attachmentName = "" // a name without bytes carries no attachment
 	}
-	_, err = svc.store.Insert(ctx, accountID, body, attachment, attachmentName, normalizeChannel(channel), parseIP(senderIP))
+	ch := normalizeChannel(channel)
+	// Snapshot the languages at submit time (acc is already loaded for the guest check):
+	// the sender's interface language, and the connector bot language when the message
+	// came through an external connector (currently Telegram).
+	var channelLang string
+	if ch == "telegram" {
+		channelLang = acc.ServiceLanguage
+	}
+	_, err = svc.store.Insert(ctx, accountID, body, attachment, attachmentName, ch, acc.PreferredLanguage, channelLang, parseIP(senderIP))
 	return err
 }