clean: archive legacy stt/tts/llm services; update ARCHITECTURE.md + README.md to current stack (REST gpt-4o-transcribe, nano, sage, Honcho, incremental TTS, white noise)

Per PLAN item 6. Legacy files moved to archive/legacy-pipeline/.

archive/legacy-pipeline/stt.py

@@ -0,0 +1,27 @@
+"""Speech-to-text via OpenAI Whisper API"""
+
+import logging
+from openai import AsyncOpenAI
+from config import settings
+
+logger = logging.getLogger("kira.stt")
+
+
+def _get_client() -> AsyncOpenAI:
+    return AsyncOpenAI(api_key=settings.openai_api_key)
+
+
+async def transcribe_audio(audio_bytes: bytes) -> str | None:
+    """Transcribe audio bytes to text using Whisper API."""
+    try:
+        client = _get_client()
+        transcript = await client.audio.transcriptions.create(
+            model="whisper-1",
+            file=("audio.webm", audio_bytes, "audio/webm"),
+            language="en",
+            response_format="text",
+        )
+        return transcript.strip() if transcript and transcript.strip() else None
+    except Exception as e:
+        logger.error(f"STT error: {e}")
+        return None