Ingest slide templates

Purpose

Turn slides from a real deck into reusable templates in the workspace's template library, fully documented and ready to pick when building a deck.

This skill chains two steps:

1. Ingest each requested slide with the CLI (ingest --slide). This clones the slide, extracts its text fields and fonts, renders a screenshot (if LibreOffice is installed), and writes a description.md TODO stub.
2. Describe each imported template by running the draft-slide-template-description workflow, which replaces that stub with a short, accurate description.

The output is one finished template folder per slide, with template.pptx, template.yml, fields.yml, an optional screenshot, and a real description.md.