One Stack Newsletter Assets

Generates two types of assets for One Stack issues:

1. Thumbnails — 1200×630 PNG via Pillow, Signal Grid aesthetic
2. Excalidraw diagrams — .excalidraw JSON files via Python

Both are written directly into the issue folder and committed if requested.

Context (always load first)

Before generating anything, read these files to absorb brand and style context:

/Users/reymerekar/Desktop/rm-agents/content/newsletter/branding/brand-book.md
/Users/reymerekar/Desktop/rm-agents/content/newsletter/branding/thumbnail-philosophy.md