fix: preserve batch/input axes in output-axis block tensor concat spec The output-axis concat spec "bt0,...; bt1,..." dropped batch and input rows, causing shape errors when list block tensor components had input or batch axes. Use the full spec "...|...-> bt0,...; ..." to broadcast batch/input rows through concatenation. Add test 13 exercising list block tensors with input-dim components. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>