v0.1.0 — pure-Swift on-device mesh healing

Liepa min-dihedral hole-fill + opening-aware selective fill + non-manifold resolve + degenerate policy on a dependency-free MeshHeal value type. Closes 99.8% of solidifiable bodies on the 3946-body reference STL, ~ms/body, non-destructive, opening-preserving. 5 tests pass.