Alternate QM₂² witnesses

Different indicator allocations of Construction QM₂² from the same [50,40] seed. Both pass the exhaustive covering check with the same rank and density as ../H_r18_n815.txt and ../H_r20_n1631.txt.

Of 815 columns at r=18, 720 are not in the primary matrix; at r=20, 1457 of 1631. The indicator assignment is a free choice, so two allocators give two distinct verifying codes.

Not used by run_all.sh. Kept as a second witness, not as a scaffold.