Adds a custom Astro loader that reads the Zola-style TOML frontmatter
(+++ ... +++) directly, so content/ stays the single source of truth
with no YAML conversion step. Defines writings/portfolio/bookshelf/
blogs collections and basic list/detail pages for each, rendering the
seed entries end-to-end (verified in-browser via `pnpm --filter site
dev`). This is the first runnable MVP: home, writings list + post
detail, portfolio, bookshelf (books and papers), and curated blogs
all render from real content/ files.
Adds content/README.md documenting the TOML frontmatter contract each
content type must follow, plus one seed entry per type to lock the
schema in a runnable form. Bookshelf entries use a kind field ("book"
or "paper") so academic papers (DOI/arXiv id) are first-class
alongside ISBN-driven books, not bolted on later.
andwati