docs: split Wandb run into Train wandb + Eval wandb (cross-project refs prefixed smol/)

docs: fix MANIFEST L4H4E128 paths after rename

docs: succinct external README + corrected MANIFEST (1:1:1:1 paths fixed)

docs: point code ref to akhljndl/smollm GitHub repo

docs: add MANIFEST.md (full 1:1:1:1 per-checkpoint provenance, 89 rows)