router: a Russian verb is a whole sentence, not thin evidence

The clarify gate thinned any one-word utterance to 0.3 confidence, which
trips the stage-3 gate and comes back as "не совсем поняла". That is an
English intuition. Russian packs subject, tense and gender into one word,
so "поужинал" is a complete report and "привет" a complete greeting, and
both got clarified.

thinSingleToken keeps the rule for bare nominals, where it is real ("вода"
is a fact-or-query coin flip), and spares two classes: a closed lexicon of
social and control singles, and any token carrying a verb ending. Both
tests are offline.

Fixture: false clarifies 3 → 2, intent-only 74.0% → 75.3%, full accuracy
unchanged at 70.1%, missed clarify still 1.

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

internal/router/llmrouter.go

@@ -194,12 +194,13 @@ func (lr *LLMRouter) Route(ctx context.Context, utterance string, now time.Time)
 		return Decision{}, false, nil
 	}
 	d := Decision{Utterance: utterance, Stage: 1, Confidence: llmFullConfidence}
-	// A single-token utterance is thin evidence: the model had nothing to
+	// A bare one-word nominal is thin evidence: the model had nothing to
 	// disambiguate on ("вода" is a fact-or-query coin flip, "бэкап" an
 	// act-or-report one) and stage 0 would already have won on anything
-	// that pattern-matches cleanly. Flag it now; router.go's stage-3 gate
-	// (Router.Route) decides whether that trips Clarify.
-	if len(strings.Fields(utterance)) <= 1 {
+	// that pattern-matches cleanly. A greeting or an inflected verb is NOT
+	// thin, however short — see thinSingleToken. Flag it now; router.go's
+	// stage-3 gate (Router.Route) decides whether that trips Clarify.
+	if thinSingleToken(utterance) {
 		d.Confidence = llmThinConfidence
 	}
 	switch Intent(a.Intent) {