fix: auto-width columns shrink when widest row is removed

[xbrxr03]

Summary

Fixes #3449 — DataTable auto-width columns do not shrink back down when the row containing the widest cell is removed.

The Bug

When remove_row() is called on a DataTable with auto-width columns, the column widths are never recalculated. This means removing the row that contained the widest cell in a column leaves the column stuck at its old width, even though all remaining rows are narrower.

This is because remove_row() deletes the row data and updates row locations, but never triggers a column width recalculation. The existing _update_column_widths() method only handles cells that were explicitly updated (via the updated_cells set), so it cannot detect when a removed row was the one setting the maximum width.

The Fix

Added _recalculate_auto_width_columns() which recomputes content_width for each auto-width column by measuring all remaining cells after row removal. Called from remove_row() after deleting the row data but before refreshing the layout.

Key behaviors:

• If no rows remain, column width collapses to just the label width
• If rows remain, column width becomes max(widest remaining cell, label width)
• Fixed-width columns (auto_width=False) are unaffected

Testing

• ✅ New test: test_remove_row_auto_width_columns_shrink — verifies that removing the widest row shrinks the column width
• ✅ All 88 existing DataTable tests pass
• ✅ Reproducible with the example app from the issue (press R to remove row, column now shrinks)

Reproduction

The original issue includes a complete reproduction app. With this fix:

1. Run the example app — columns are sized to fit the widest content
2. Press R to remove the row with "Aleksandr Sadovnikov =============" (the widest cell)
3. Before fix: Column stays wide ✗
4. After fix: Column shrinks to fit remaining content ✓

[willmcgugan]

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