maven: dedupe knowledge prompt to router.KnowledgePrompt (task 4 follow-up)

Task 4 created and tested router.KnowledgePrompt() but the live path in
LLMPhraser.PhraseQuery used a separate hardcoded copy of the same RU
anti-hallucination prompt, leaving KnowledgePrompt() as dead code and two
strings that could drift. Point the phraser at the tested helper so there
is a single source of truth.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/phraser/llmphraser.go

@@ -16,6 +16,7 @@ import (
 
 	"github.com/kami/maven/internal/delivery"
 	"github.com/kami/maven/internal/loop"
+	"github.com/kami/maven/internal/router"
 )
 
 var listenRE = regexp.MustCompile(`listening on (https?://\S+)`)
@@ -171,8 +172,9 @@ func (p *LLMPhraser) PhraseNudge(ctx context.Context, c loop.Candidate) (deliver
 // LLM error — better to give the raw data than silence.
 func (p *LLMPhraser) PhraseQuery(ctx context.Context, utterance string, notes []string) (string, error) {
 	if len(notes) == 0 {
-		// General knowledge — no notes to ground the answer
-		sys := "Ты — Мавена, персональный ассистент. Ответь кратко из своих знаний. Если не знаешь — скажи \"не знаю\". Не выдумывай."
+		// General knowledge — no notes to ground the answer. The system
+		// prompt is the single tested source in router.KnowledgePrompt.
+		sys := router.KnowledgePrompt()
 		prompt := fmt.Sprintf("Пользователь спрашивает: \"%s\".", utterance)
 		resp, err := p.chatWithSystem(ctx, sys, prompt, 256)
 		if err != nil || resp == "" {