Null-Homologous Curves and the Cauchy Integral Theorem

Barrel file re-exporting the three submodules:

• Basic — IsNullHomologous, FTC for piecewise C¹ contours, convexity bridge
• DixonProof — Dixon's proof: h₁, h₂, Liouville, Cauchy integral formula
• Meromorphic — meromorphic contour integral vanishing, higher-order cancellation