fix(docx): recognize character-relative first-line indents

[Bortlesboat]

Problem

view issues reports that a Normal-style body paragraph is missing a first-line indent even when its OOXML indentation has a positive firstLineChars value.

Fix

Treat either a non-zero absolute FirstLine value or a positive character-relative FirstLineChars value as satisfying the existing first-line-indent check. The current hanging-indent, alignment, list, and text exemptions are unchanged.

Validation

• Built src/officecli/officecli.csproj in Release with .NET 10.
• Reproduced the false warning with firstLineChars=200 before the change and confirmed it is absent afterward.
• Confirmed firstLineChars=0 still reports the warning.
• Confirmed firstLineIndent=2cm remains accepted.
• Confirmed all generated DOCX fixtures pass officecli validate --json.

Closes #283.