v0.13.1: See the slides, share the skill

v0.13.1 - See the slides, share the skill

This is a showcase and distribution update with a small readability repair,
not a new layout engine or a model benchmark.

• The README previews fewer, larger actual slides: lab evidence and tables,
  editorial storytelling and a full-slide metric, and operational processes
  and decisions. The earlier library editorial source is rebuilt unchanged
  with the current renderer, rather than presented as an old screenshot.
• Agent discovery metadata is current and ships with both the skill package
  and Codex plugin. Install links, public listing information, and sharing
  copy distinguish a repository marketplace from official public approval.
• A small deterministic export prepares the skills-only plugin ZIP for the
  official submission route. Local marketplace screenshots stay available;
  the public-upload export follows its separate metadata requirements.
• Small provenance and page-number text on dark KPI slides now honors the
  actual slide background and selects a readable footer color. Source content
  and layout stay unchanged.

All showcase scenarios are synthetic. The release includes the rebuilt
library deck and source; the other four editable decks remain in the
v0.13 design-studies download.

npx skills add https://github.com/siril9/presentation-skill --skill presentation-skill
codex plugin marketplace add siril9/presentation-skill --ref v0.13.1

The skill remains MIT-licensed and model-flexible. The public plugin ZIP is a
submission artifact, not evidence of OpenAI approval or directory publication.