Chapter IV pivot backend: for each (team, project) pair in the given
work-logs queryset, counts distinct work-log dates. Returns columns
(projects), rows (teams with cell dict), column totals, and grand total
ready for direct template rendering.
Logs with NULL team or NULL project are excluded (can't pivot on NULL).
Teams/projects with zero activity don't appear as rows/columns — keeps
the pivot tight.
Tests cover shape, cell counts, row+column+grand totals, and
zero-activity team omission.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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