fix(pptx): honor noFill text outlines in HTML preview

[y4ho0]

Summary

• skip CSS glyph strokes when a run-level text outline explicitly contains a:noFill
• preserve the existing rendering path for solid and implicit text outlines

Scope

This addresses only the a:rPr/a:ln/a:noFill text-outline item in #341. The connector, inherited alignment, and equation-rendering items in that issue remain out of scope.

Refs #341

Validation

• dotnet build src/officecli/officecli.csproj --configuration Release --no-restore — passed with 0 errors (one pre-existing nullable warning in ExcelHandler.SheetShift.cs)
• rendered the public sample.pptx from [PPTX] view html does not preserve several drawing, text, and equation properties #341: before this change the affected run emitted a black -webkit-text-stroke; after the change it emits no text stroke
• negative control: replacing the same outline with a 1 pt red solid outline still emits -webkit-text-stroke:1.33px #FF0000
• git diff --check