Sheet names starting with '.' or reading as R1C1 (R, C, RC, R1C1...) were saved
unquoted, so Excel could not open the file; PivotTable sources and ADDRESS left
cell-like names (A1) bare. The quoting rule, unquoting and sheet splitting now
live once in gridcraft_core::addr and replace the copies in the formula printer,
pivot, ADDRESS, chart, xlsx, Solver, Go To and the Name Box (which now reads ''
as ').
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
