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/postgres/jet/backend/model/feedback_messages.go

@@ -20,6 +20,8 @@ type FeedbackMessages struct {
 	AttachmentName *string
 	SenderIP       *string
 	Channel        string
+	Lang           *string
+	ChannelLang    *string
 	ReadAt         *time.Time
 	ArchivedAt     *time.Time
 	ReplyBody      *string