feat: LLM router with chat intent and Cyrillic wake-word support

- Add LLMRouter: grammar-constrained LFM call for intent classification
  after stage-0, before classifier cascade. Errors fall through gracefully.
- Add IntentChat: conversational intent with no store side-effect, routed
  through LLM -> phraser chat endpoint.
- Extract slots for Chat: no structured slots, full utterance is payload.
- Extend stage-0 grammars to fire through Cyrillic wake-word spellings
  (Мэйвен/Мейвен/Майвен/etc.) produced by Russian STT model.
- StripWakeToken helper strips leading wake in any script so time/date
  grammars still match when wake is present.
- Add classifier examples for chat utterances (EN + RU).
- Wire LLMRouter into Router.Config; optional, nil-safe.

internal/voice/replier.go

@@ -78,6 +78,8 @@ func (s *StubReplier) Reply(d router.Decision) string {
 		return "сохранила заметку."
 	case router.IntentQuery:
 		return "поискала в заметках — ничего не нашла."
+	case router.IntentChat:
+		return "поговорили." // stub — LLMReplier replaces this
 	default:
 		return "приняла."
 	}