🧪 test: add unit tests for createRenderedImagePdf

[MarsLuay]

Add comprehensive unit tests for createRenderedImagePdf in renderedPdfExport.ts covering single-page, multi-page, text run formatting, WinAnsi encoding, and xref byte offsets.

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PR created automatically by Jules for task 11568117517293570391 started by @MarsLuay

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