docs: add Cursor Cloud dev environment notes to AGENTS.md

[aggre]

Summary

Sets up and verifies the development environment for this content-only repo, and records durable, non-obvious notes for future Cursor Cloud agents.

This is a content-only repository (markdown blog posts consumed by lemmaoracle/lemma at build time). There is no server, application, or automated test suite — the only tooling is Prettier via pnpm.

What was verified

• pnpm install — installs prettier@3.8.1 (Node 22 / pnpm 10 already present).
• pnpm format:check (the "lint") — runs correctly; reports pre-existing formatting warnings across ~649 files (repo is intentionally not fully Prettier-clean). Not modified.
• Core authoring workflow — created a scratch post per the repo's frontmatter conventions, confirmed prettier --check flagged it, prettier --write reformatted it, and --check then passed. Scratch file removed (not committed).

Changes

• AGENTS.md: added a ## Cursor Cloud specific instructions section documenting that this is a content-only repo (no app/tests), where the standard commands live, that format:check has many pre-existing warnings (don't mass-reformat), and that CI only triggers a Cloudflare redeploy on push to main.

The update script (pnpm install) is configured separately for VM startup.