Improve local startup checks and Korean STT defaults

.env.example

@@ -11,11 +11,11 @@ LOCAL_AI_VENV_PATH=.local-ai/.venv
 LOCAL_AI_CACHE_DIR=.local-ai/cache
 # Windows면 `python` 또는 `py -3`
 LOCAL_AI_PYTHON=
-LOCAL_STT_MODEL=tiny
+LOCAL_STT_MODEL=small
 # CUDA dll 오류가 나면 `cpu`
 LOCAL_STT_DEVICE=auto
 LOCAL_STT_COMPUTE_TYPE=auto
-LOCAL_STT_BEAM_SIZE=1
+LOCAL_STT_BEAM_SIZE=3
 LOCAL_TTS_MODEL_PATH=.local-ai/models/kokoro-v1.0.onnx
 LOCAL_TTS_VOICES_PATH=.local-ai/models/voices-v1.0.bin
 LOCAL_TTS_LANGUAGE=ko