docs(cli): Document General format scientific notation behavior #177

Summary

Users are surprised when long decimal numbers display in scientific notation. This is expected Excel behavior, not a bug, but needs documentation.

Severity: Low | Effort: Trivial

Current Behavior

xl -f in.xlsx view A1
# A1 contains: 0.123456789012
# Output: 1.234568E-01

Root Cause (Not a Bug)

NumFmtFormatter.formatGeneral() intentionally switches to scientific notation when string length > 11 characters:

// NumFmtFormatter.scala lines 127-133
if str.length > 11 then f"${n.toDouble}%.6E"

This matches Excel's General format behavior and is independent of column width.

Workaround

Users should apply explicit NumFmt for financial precision:

xl -f in.xlsx -o out.xlsx style A1 --num-fmt number

Action Items

• Add note to CLI help for view command explaining General format behavior
• Add example in docs/reference/cli.md showing how to preserve decimal display
• Consider adding a --format precision option for view command (separate enhancement)

Key Files

• xl-core/src/com/tjclp/xl/display/NumFmtFormatter.scala (lines 127-133)
• docs/reference/cli.md