Render square Wang solutions as hexagons

[xtraid]

Summary

• formalize the Basire/Culik square-to-hex port as a pure renderer transformation with a raster-independent checker
• preserve the existing square renderer byte-for-byte by adding hex output only behind the --hex flag on the same command
• render pointy-top axial hexagons from the existing square v1 witness, including negative coordinates, holes, dynamic dimensions, and a pixel-stable golden
• document the algebraic mapping, inverse projection, correctness boundary, and provenance

Correctness boundary

The renderer still consumes only wang-solution-v1. This change adds no hex solver, hex schema, intermediate serialization, or core dependency. The checker verifies the exact six-edge port and adjacency equivalence; it does not claim to validate SAT independently of the existing square witness contract.

Verification

• 213 renderer tests, including all 144 legacy tests and 24 focused hex tests
• 94 root Python tests and all 16 C test binaries through make check
• native and cross-engine smoke checks
• strict GCC and Clang checks
• Pages validation for 22 technical documents and all literal internal links
• clean diff, secret scan, and artifact scan