v8 updates

[rbarrue]

Main changes/additions:

• shape-only systematic variations
• TFMC and PNN closure plots done only on the final_eval partition for a more "proper" evaluation
• code to check for and reweight HT mismodelling in DY HT-binned sample (not used)
• code to plot chi2(variation, nominal) from surrogate outputs in 1D distributions of surrogate input variations
• CLAUDE.md file generated together with Claude (/init command).

Also made a few changes to the folders where plots are stored.

v8 configs are still in flux, so will keep this PR as a draft.