fix: remove all nested duplicate folders

sync: hf-space is now the single source of truth

fix: Gradio mount, verifier stage3, poc_history clear, real notebook

fix: STAGE_FILES points stages 2-3 to actual app files + update reward_curve (LFS) + results table

fix: png rename + remove placeholder + fix blog link + add baseline comparison

fix: rename reward curve to .png to match README