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/.

backend/services/llm.py

@@ -1,30 +0,0 @@
-"""LLM service — DeepSeek API"""
-
-import logging
-from openai import AsyncOpenAI
-from config import settings
-
-logger = logging.getLogger("kira.llm")
-
-
-def _get_client() -> AsyncOpenAI:
-    return AsyncOpenAI(
-        api_key=settings.deepseek_api_key,
-        base_url=settings.deepseek_base_url,
-    )
-
-
-async def get_kira_response(messages: list[dict]) -> str:
-    """Get Kira's response from the LLM."""
-    try:
-        client = _get_client()
-        resp = await client.chat.completions.create(
-            model=settings.deepseek_model,
-            messages=messages,
-            max_tokens=300,
-            temperature=0.7,
-        )
-        return resp.choices[0].message.content or "Mhm, I'm here!"
-    except Exception as e:
-        logger.error(f"LLM error: {e}")
-        return "I'm still here with you! Could you say that again?"

backend/services/stt.py

@@ -1,27 +0,0 @@
-"""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

backend/services/tts.py

@@ -1,31 +0,0 @@
-"""Text-to-speech via OpenAI TTS API"""
-
-import logging
-from openai import AsyncOpenAI
-from config import settings
-
-logger = logging.getLogger("kira.tts")
-
-
-def _get_client() -> AsyncOpenAI:
-    return AsyncOpenAI(api_key=settings.openai_api_key)
-
-
-async def synthesize_speech(text: str, voice: str = "nova") -> bytes:
-    """Synthesize text to speech audio bytes.
-    
-    Voices available: alloy, echo, fable, nova, shimmer
-    Nova is the warmest female voice — fits Kira's personality.
-    """
-    try:
-        client = _get_client()
-        resp = await client.audio.speech.create(
-            model="tts-1",
-            voice=voice,
-            input=text,
-            response_format="opus",
-        )
-        return resp.content
-    except Exception as e:
-        logger.error(f"TTS error: {e}")
-        return b""