swi_iceberg: A Robust Six-Band MADN Visualization for the Iceberg Fleet

Design specification of the swi_iceberg, a robust six-band distribution mark for the iceberg fleet: each object's samples are summarized around the median and scaled by MADN (1.4826 x median absolute deviation); six equal bands over +/-3 MADN encode population as band width and the observed value range as band height; samples beyond the envelope are retained as topping/bottoming; objects float on a shared absolute axis and the pooled distribution is drawn as a self-similar, globally clipped background. Includes naming and provenance, statistical invariants, edge cases, and relation to prior work. The related repository holds the Apache-2.0 reference implementation; this record covers the specification text and figures under CC BY 4.0.