feed questions ask the seeds, not a stem list (V-522)

Whether a turn is about the feeds is a question about meaning, and
internal/router/feeds.go was deciding it with three word lists. Their own
comments admit the shape: vagueNouns exists because "что нового?" is the most
common opener in the language and it matched a feed noun, so a daemon with no
feeds block answered a greeting with a configuration status.

So topicFeed joins the four subjects in cmd/mavend/topics.go and queryFeeds
calls turnIsAbout. The word lists stay as the offline floor, reached through
feedFloor, and they are allowed to stay narrow now that they are not the only
answer. The category is not a recogniser — a topic is marked by a preposition —
so it comes out of the utterance either way, through the new
router.FeedCategoryOf.

The greeting is handled by the shape rather than by a bail-out list. "что
нового" is a topicOther seed, close enough to the feed seeds that a bare
"что нового?" cannot clear topicMargin, and a thin call goes to
ParseFeedQuery, which declines a vague noun with no topic beside it.

Measured on TestONNXTopics, four held-out cases added: 23/23, and no case that
passed before it regressed. One seed pair was added during the measurement,
because "какие сегодня заголовки" first read as weather — "какая сегодня
погода" was the nearest thing in the whole set carrying "сегодня".

cmd/mavend/topics.go

@@ -9,7 +9,7 @@ import (
 )
 
 // Which subject is this question about — the weather, the house, the LAN, what
-// needs looking at, or none of them. Third of the three mechanisms replacing hand-written Russian
+// needs looking at, his feeds, or none of them. Third of the three mechanisms replacing hand-written Russian
 // patterns (Vikunja #522, owner's call 2026-08-04). internal/lexicon holds the
 // sets that can be finished and internal/morph answers the grammar questions;
 // this is for the sets that can never be finished, because "is this about the
@@ -37,6 +37,11 @@ import (
 // внимания", which is Praxis's operational state and reached the web search
 // before the source existed (Vikunja #475).
 //
+// A fifth joined on 05-08-2026: the feeds, "что нового в лентах". Its word lists
+// were the last pair of hand-written Russian stem lists in the router (V-522),
+// and they carried the same admission in their own comments — vagueNouns exists
+// because "что нового?" is a greeting that matched a feed noun.
+//
 // The regexes stay as the offline floor, unchanged, for a handler with no
 // embedder or a turn whose vector never got computed. They are allowed to remain
 // narrow now precisely because they are no longer the only answer.
@@ -52,6 +57,7 @@ const (
 	topicHome    topicLabel = "home"
 	topicNetwork topicLabel = "network"
 	topicAttend  topicLabel = "attention"
+	topicFeed    topicLabel = "feeds"
 	topicOther   topicLabel = "other"
 )
 
@@ -117,7 +123,30 @@ var topicSeedSets = map[topicLabel][]string{
 		"what needs attention",
 		"what needs looking at right now",
 	},
+	topicFeed: {
+		"что нового в лентах",
+		"какие новости",
+		"что нового по технологиям",
+		"почитай заголовки",
+		// Two seeds carrying a day word beside the headlines. Without them
+		// "какие сегодня заголовки" read as weather, because "какая сегодня
+		// погода" is the nearest thing in the whole set with "сегодня" in it.
+		"заголовки за сегодня",
+		"какие главные новости за день",
+		"покажи новости за сегодня",
+		"что пишут в новостях",
+		"что нового про политику",
+		"расскажи что нового в ленте",
+		"what is new in the feeds",
+		"any news headlines today",
+	},
 	topicOther: {
+		// 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
+		// ParseFeedQuery, which declines a vague noun with no topic beside it.
+		"что нового",
+		"как дела",
 		// Complaints, which are not requests to scan or to read the house.
 		// isNetworkQuery's comment names this one: a scan she runs unasked is
 		// the noisy behaviour the bounds exist to prevent.