Replace hardcoded /tmp/{provider} default paths with XDG-compliant persistent
directories (~/.local/share/mem0/{provider}), fixing failures on Windows,
macOS LaunchAgents, Linux systemd, and Docker. Adds MEM0_DATA_DIR env var
override, legacy /tmp data migration warning, and updates Qdrant/ChromaDB/FAISS
configs and docs to use the new defaults.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>