Demo firmware runs clean decode + noisy decode (vector 0) and reports
pass/fail on GPIO[7:0]. All 5 cocotb tests pass: ldpc_basic, ldpc_noisy,
ldpc_max_iter, ldpc_back_to_back, and ldpc_demo.
Also adds .cf/project.json with GPIO configuration.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
