RTL fixes: - Skip unconnected columns (H_BASE=-1) in LAYER_READ/WRITE/SYNDROME - Set unconnected VN->CN messages to +MAX (not 0) to avoid corrupting min-sum minimum computation - Add SYNDROME_DONE state to fix timing race on syndrome_ok - Fix VERSION_ID hex literal (0xLD01 -> 0x1D01) Testbench verifies VERSION register read and clean all-zero decode. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>