Add fully local conversational AI pipeline for Reachy Mini

Local STT (Qwen3-ASR), VLM (Gemma 4 26B-A4B), and TTS (Spark-TTS) running
on Apple Silicon via MLX, with bracket-tag action system for nod, shake,
wiggle, dance, photo, and pre-recorded emotions.

run.sh

@@ -0,0 +1,3 @@
+#!/bin/bash
+cd "$(dirname "$0")"
+exec .venv/bin/python conversation.py "$@"