continuation: only an ellipsis may widen the keyword match

Deployed check, second round: "привет" after "какой сегодня день" answered
with the date. followUpMerge fills an empty Text from the previous
same-intent turn, so the topic-widening added a minute earlier was reading
an inherited topic on turns that had nothing to do with it.

Decision gains Continued, set only by continuation.go and never by the
router. replySystem widens on that and nothing else, so an inherited Text
is back to being invisible.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TrVSBKe3RFDF4fGYKWYQnX

cmd/mavend/continuation.go

@@ -82,6 +82,7 @@ func continuationDecision(prev *dialogue.Session, text string, now time.Time) (r
 		Intent:     router.Intent(prev.Intent),
 		Confidence: 1.0,
 		Stage:      0,
+		Continued:  true,
 		Slots: router.Slots{
 			Key:    prev.Slots.Key,
 			HasKey: prev.Slots.HasKey,