list read-back asks the seeds; add and clear keep their tables (V-522)

internal/router/list.go was the last file on the sweep, and the answer is a
split rather than one mechanism. What the four paths need is different, and the
V-529 comment in the file already had half of the argument.

Reading a list back needs one bit — is this about the list — so topicList joins
the subjects in cmd/mavend/topics.go and queryList calls turnIsAbout.
listQueryPrefixes stays as the offline floor. Which list he named is a noun in
the dictionary either way, through the new router.ListNamedIn, which scans the
whole utterance: the seeds claim a read-back without eating a prefix, so "что
мне нужно в аптеке" has nothing for takeListTag to read the front of.

The other three keep their phrase tables, and the header says why. Add and
remove have to know WHERE the item starts, and a cosine over a whole utterance
does not say which byte the milk begins at. Clear deletes the list, so a false
claim loses rows he cannot get back — that is not the trade a margin makes.

Measured on TestONNXTopics, four held-out cases added: 27/27, no case
regressed. Two existing margins moved by under a hundredth because the new
seeds became the runner-up, both still far clear of topicMargin.

cmd/mavend/topics.go

@@ -58,6 +58,7 @@ const (
 	topicNetwork topicLabel = "network"
 	topicAttend  topicLabel = "attention"
 	topicFeed    topicLabel = "feeds"
+	topicList    topicLabel = "list"
 	topicOther   topicLabel = "other"
 )
 
@@ -140,7 +141,25 @@ var topicSeedSets = map[topicLabel][]string{
 		"what is new in the feeds",
 		"any news headlines today",
 	},
+	// Reading a standing list back, and only that. Adding to one and clearing
+	// one stay on the phrase tables in internal/router/list.go — see its header
+	// for why a span and a delete are not seed-shaped work.
+	topicList: {
+		"что в списке покупок",
+		"что мне нужно купить",
+		"прочитай список покупок",
+		"покажи что в списке",
+		"что осталось купить в магазине",
+		"что мне нужно в аптеке",
+		"какой у меня список покупок",
+		"what is on my shopping list",
+		"read me the grocery list",
+	},
 	topicOther: {
+		// A task question is not a list read-back. They collide on "что у меня",
+		// and the list has its own table to lose to as well.
+		"какие у меня задачи",
+		"что у меня в делах",
 		// The bare newness opener, which is a greeting and not a request for
 		// headlines. It sits here on purpose: it is close enough to the feed
 		// seeds that it will not clear topicMargin, and a thin call goes to