docs: add heading and improve README spacing

docs: add sample Excel VaR reports for traceability

fix: update lookback_days to 253 for accurate VaR estimation

fix: add environment-aware logging with prod/dev/test levels and fix CSS not applying in Gradio 6

feat: enhance Gradio UI with portfolio footer and update launch configuration

docs: add HF Spaces deployment, LFS setup, and update README with screenshot and install instructions

feat: initial implementation of VaR engine