[KnifeLemon]

Summary

For #96: converts PDF to PowerPoint, one slide per page. Each slide shows the page rendered as a picture, so it looks exactly like the PDF but can't be edited. Built in; no new engine.

• New pdf-slides engine (PdfSlidesConverter, PictureDeckWriter).
  • Pages are rendered with PDFium at the preset's DPI (150–600; very large pages get a lower DPI) and the preset's page range.
  • Each page becomes a JPEG at the preset's quality (default 90).
  • The PPTX package is written directly, slide by slide, so pages aren't held in memory.
• Slide size follows the first page: A4 portrait gives portrait slides, 16:9 gives widescreen. Every page is fitted and centred on its slide, and rotated pages are handled.
• Speaker notes hold each page's text, so it can be searched and copied. Scanned pages get no notes.
• Routing: the new ConversionEdge.DirectOnly flag means this edge is used only for a direct PDF → PPTX conversion, never as a step in longer routes (DOCX → PDF → PPTX, PDF → PPTX → ODP). An exhaustive test checks that every other format pair keeps its route.
• Preset "PPTX (slides)" goes on the PDF donut after DOCX. The donut was full at 12 slices, so the new default drops TIFF from it; the TIFF preset itself is kept. Settings schema 18 updates untouched PDF donuts and adds the preset to customised ones only when there is room.
• Encrypted PDFs fail with the usual password message. A broken PDF fails without leaving a file.

Test plan

• 14 new PdfSlidesTests, checked with OpenXmlValidator (0 errors) and read back with Filee's PPTX reader. Route stability is checked across all format pairs.
• Core 204, Engines 835, Cli 21 and App 265 tests passed. dotnet format is clean.
• Not opened in PowerPoint, Impress or Keynote yet.

🤖 Generated with Claude Code