For non-exclusive support-message category heatmaps, do not sum distinct issue counts

For non-exclusive support-message category heatmaps, do not sum distinct issue counts from issue-type/category strata. Produce a pre-deduplicated matrix keyed by canonical step, direction, and lexical category, with the category’s distinct issue count plus an exact step-direction denominator. Render each cell as a count and within-direction prevalence, explicitly stating that categories can overlap; this preserves count semantics without falsely implying a 100% composition.