Ghost OS v2.1.2

Pin vision sidecar dependencies for reliable ghost_ground.

What changed:

• Pin mlx-vlm==0.1.15 (with --no-deps) and transformers==4.48.3
• transformers>=4.49 requires PyTorch for Qwen2VL video processor, breaking MLX-only environments
• ghost setup now recreates the Python venv on upgrade (version stamp)
• ghost doctor flags incompatible transformers versions
• Vision sidecar diagnoses dependency errors at startup

Upgrade:

brew upgrade ghost-os
ghost setup

ghost setup will recreate the Python environment with pinned deps. Verify with ghost doctor.

Fixes #7