Prepare app for Hugging Face Spaces deployment

Anchor research-informed retirement equity share to Duarte et al.'s own findings

Ground research-informed allocation in Duarte et al./Choi/Choi-Liu-Liu

Add research-informed allocation as a third method

Make mean-variance optimization respond to risk tolerance and horizon

Fix lifecycle glide-path typo and build Gradio interface on the portfolio engine

Add baseline portfolio engine: lifecycle heuristic and mean-variance optimization

Allow opting into a public Gradio share link via env var

Add minimal Gradio app scaffold for DCF valuation tool