Add ghost formula

[chailandau]

What

Adds a ghost formula so the Block Ghost CLI can be installed via the OSS tap:

brew install block/tap/ghost

Ghost is product-surface composition tooling for AI agents — fingerprints, deterministic checks, advisory review, and comparison. Source: block/ghost.

How it installs

The release artifact is the published npm tarball (anarchitecture-ghost-<version>.tgz), which extracts to a package/ directory containing the built dist/ and package.json. The formula:

1. Installs package/* into libexec.
2. Runs npm install --omit=dev for the runtime deps — all pure-JS, so there's no native-module / bottle-relocation concern.
3. Symlinks dist/bin.js onto the PATH as ghost.

depends_on "node".

Pinned release

Pinned to a real, published release artifact:

• tag: anarchitecture-ghost@0.11.1
• url: https://github.com/block/ghost/releases/download/anarchitecture-ghost@0.11.1/anarchitecture-ghost-0.11.1.tgz
• sha256: 940bb6a9008598a11e70a0ee67753a722770ef75099e2711e46de52a73a5e5b6 (verified against the downloaded GitHub Release asset)

The block/ghost release pipeline now cuts npm + GitHub Release + .tgz from a single Changesets publish, so this url/sha256 resolve to a live artifact and the formula is installable.

Auto-bump wiring

Modeled on Formula/sessh.rb. The header comment documents the bump invocation. Until the source-repo autobump is wired (its GitHub App secrets are not yet configured), the formula can be bumped manually:

gh workflow run bump-formula.yaml --repo block/homebrew-tap \
  -f repo=block/ghost -f formula=ghost \
  -f tag=anarchitecture-ghost@<X.Y.Z> \
  -f artifact_url=https://github.com/block/ghost/releases/download/anarchitecture-ghost@<X.Y.Z>/anarchitecture-ghost-<X.Y.Z>.tgz

Ready for review — the pinned release exists and the sha256 is verified.