Add prune_empty feature to hide empty rows/columns in pivot mode.
View gains prune_empty boolean (default false for backward compat).
GridLayout::prune_empty() removes data rows where all columns are
empty and data columns where all rows are empty.
Group headers are preserved if at least one data item survives.
In records mode, pruning is skipped (user drilled in to see all data).
EditOrDrill command updated to check for regular (non-virtual)
categories when determining if a cell is aggregated.
Co-Authored-By: fiddlerwoaroof/git-smart-commit (unsloth/Qwen3.5-35B-A3B-GGUF:Q5_K_M)
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