4d2e3957c3
Move to boot.fth: D+, D-, DNEGATE, DABS, D0=, D0<, D=, D<, D2*, D2/, DMAX, DMIN, M+, DU<. D+ uses proper carry detection via unsigned comparison after low-cell addition. All other double-cell words build on D+ and standard Forth stack operations. Removed 544 lines of Rust closures. Cumulative: ~1,091 Rust lines removed across Phases 1-2, replaced by ~80 lines of Forth. All 425 tests pass.