Render square Wang solutions as diagnostic PNGs

[xtraid]

Summary

• add a presentation-only square renderer and CLI for wang-solution-v1
• derive deterministic integer-only N/E/S/W assets with an injective RGB palette
• support negative bounds, holes, dynamic sizing, atomic PNG output, and a decoded-pixel golden
• preserve the legacy PAP implementation, dependencies, lockfile, workflow, schema, C, and root Python unchanged

Validation

• 45 focused Wang renderer tests
• 144 preserved legacy tests; 189 combined renderer tests
• make check: 91 Python tests, 16 C binaries, Pages, native and cross-engine smoke gates
• independent review completed with its JSON failure-path finding fixed and no open findings
• post-rebase range-diff and tree equality verified; 45 focused tests rerun

Out of scope

• Wang correctness decisions, solver or exporter CLI, hex rendering, legends or fonts, and new dependencies