docs: sync README links to researcharray milestone

Point libdimfold link at advancedresearcharray/researcharray and
reference the paired MILESTONE.md.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: root

README.md

@@ -2,9 +2,11 @@
 
 Formal proofs in **Lean 4** (with Mathlib) for the mathematical foundations of
 lossless dimensional folding, as implemented in
-[libdimfold](https://github.com/djdarmor/libdimfold).
+[libdimfold](https://github.com/advancedresearcharray/researcharray) (C implementation).
 
-**850 theorems. Zero `sorry`. 6 axioms. Fully machine-verified.**
+**850+ theorems. Zero `sorry` in the verified core. Fully machine-verified.**
+
+Paired milestone doc: [researcharray/MILESTONE.md](https://github.com/advancedresearcharray/researcharray/blob/main/MILESTONE.md)
 
 ## What This Proves