Cross-platform: Windows, Linux, Intel Mac evaluation

[thedavidweng]

Problem

OpenLoop is macOS Apple Silicon only. No documented feasibility for Windows, Linux, or Intel Mac. The ACE-Step backend (MLX-based) has platform-specific constraints that need evaluation before committing to cross-platform work.

Scope

• Evaluate Windows support: MLX absence, PyTorch CPU/CUDA fallback path
• Evaluate Linux support: AppImage or Flatpak packaging, backend compatibility
• Evaluate Intel Mac: ACE-Step CPU performance viability
• Produce ADR docs/adr/0005-platform-roadmap.md with findings and recommendations

Acceptance criteria

• Each platform has a feasibility assessment with concrete findings
• docs/adr/0005-platform-roadmap.md documents support tiers and blockers
• Recommendation includes effort estimates and external dependencies