Refresh root meta files after the protectjs → stack rename

[coderdan]

Problem

The root meta files never caught up with three structural changes: the repo rename (cipherstash/protectjs → cipherstash/stack), the removal of the in-repo docs/ tree in favour of cipherstash.com/docs, and the growth of the package set (cli, wizard, migrate, prisma-next, bench).

Concretely:

• SECURITY.md had badly stale supported-version tables (e.g. stack 0.4.x vs actual 0.18.0), was missing four published packages, scoped itself to the old repo name and the @cipherstash/protect* npm namespace only, and misdescribed release auth (claimed an NPM_TOKEN; release.yml uses OIDC trusted publishing with no token).
• AGENTS.md described the pre-rename repo: five packages missing from the layout, a stale examples list, 15+ dead docs/* links, an incomplete subpath-exports list, and out-of-date bundling guidance (predating @cipherstash/stack/wasm-inline).
• CONTRIBUTE.md was still written for @cipherstash/protect in the protectjs repo (including a JSEQL mention).
• Root package.json was still named @cipherstash/protectjs with protectjs URLs, and wasn't marked private.
• .cursorrules documented the pre-rename API (protect(), csTable/csColumn, pnpm 9.x).
• The org contact email appeared as hello@cipherstash.com in 10 package.json files — correct address is humans@cipherstash.com.

Resolution

Addressed in #552 (root meta files) with the published-package README counterpart in #553. Root README.md is handled separately in #526.