feat(notifier): push state events to Smart Home Tablet overlay

Adds a thin HTTP bridge so the tablet at https://tablet.digital-home.site
shows a Siri-style overlay reflecting the current assistant state
(wake / command / response / idle / error). Non-fatal: if the tablet
is offline or TABLET_URL/VOICE_API_KEY are unset, events are silently
skipped and the assistant keeps working.

- satellite/notifier.py — POST /api/voice/event with bearer token,
  reused requests.Session for keep-alive, 1.5s timeout
- satellite/modes.py — emits wake on activation, command after STT,
  response after LLM, idle on timeout
- satellite/llm.py — emits error on gateway connection/timeout/HTTP
- .env.example documents TABLET_URL and VOICE_API_KEY

Tablet side (separate repo smart-home-tablet, commit 51c3d60) exposes
POST /api/voice/event + GET /api/voice/stream (SSE) and renders a
full-screen overlay in components/VoiceOverlay.tsx.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

satellite/notifier.py

@@ -0,0 +1,60 @@
+"""
+Tablet notifier — пересылает состояния ассистента в Smart Home Tablet
+(https://tablet.digital-home.site/api/voice/event).
+
+Планшет показывает оверлей (Siri-blob, распознанный текст, ответ).
+Не критичный слой: любые сетевые ошибки глотаются, ассистент продолжает
+работать даже если планшет оффлайн / не настроен.
+
+Активируется только когда заполнены TABLET_URL и VOICE_API_KEY в .env.
+"""
+import os
+import requests
+
+from .config import log
+
+TABLET_URL = os.getenv("TABLET_URL", "").rstrip("/")
+VOICE_API_KEY = os.getenv("VOICE_API_KEY", "")
+
+# Переиспользуем HTTP сессию (keep-alive) для минимума latency
+_session = requests.Session()
+
+_ENABLED = bool(TABLET_URL and VOICE_API_KEY)
+if _ENABLED:
+    print(f"🔔 Notifier: планшет {TABLET_URL}")
+else:
+    print("🔕 Notifier: отключён (нет TABLET_URL или VOICE_API_KEY в .env)")
+
+
+def _send(event: str, **payload):
+    if not _ENABLED:
+        return
+    try:
+        _session.post(
+            f"{TABLET_URL}/api/voice/event",
+            json={"event": event, **payload},
+            headers={"Authorization": f"Bearer {VOICE_API_KEY}"},
+            timeout=1.5,
+        )
+    except requests.RequestException:
+        log.debug("Tablet notify failed (non-fatal)", exc_info=True)
+
+
+def wake(agent_id: str):
+    _send("wake", agent=agent_id)
+
+
+def command(text: str, agent_id: str):
+    _send("command", text=text, agent=agent_id)
+
+
+def response(text: str, agent_id: str):
+    _send("response", text=text, agent=agent_id)
+
+
+def idle():
+    _send("idle")
+
+
+def error(text: str, agent_id: str = "cosmo"):
+    _send("error", text=text, agent=agent_id)