ci: publish a Homebrew cask instead of a deprecated formula

[patramsey]

brews: has been deprecated for a while. GoReleaser's own description of what it produced is "hackyish formulas that would install the pre-compiled binaries" — a formula is meant to build from source, and this project ships binaries. A cask is the supported shape.

I nearly didn't do this, and my reason was wrong

I argued against migrating on the belief that casks are macOS-only, so it would silently drop the Linux Homebrew support the README advertises. That belief is out of date. From Homebrew's source on this machine:

# cask/cask.rb:260
def supports_linux?
  return true if depends_on.requires_linux?
  !depends_on.requires_macos?     # ← Linux-capable unless it opts out
end

cask/dsl.rb documents per-OS on_macos/on_linux blocks with their own sha256, and installer.rb has a "This cask requires Linux." path. GoReleaser's deprecation note said exactly this — "this was the only way for Linuxbrew at the time, but this is no longer true" — and I second-guessed it instead of checking.

Verified, not assumed

A snapshot build writes dist/homebrew/Casks/namecom.rb containing:

on_linux do
  on_intel do
    url ".../namecom_linux_amd64.tar.gz"
  end
  on_arm do
    url ".../namecom_linux_arm64.tar.gz"
  end
end

No depends_on macos anywhere — which is precisely the condition supports_linux? tests. Same four platforms as the formula it replaces, same URLs. ruby -c on the generated file: Syntax OK.

goreleaser check is clean for the first time

That took two steps, not one: homebrew_casks.binary is itself deprecated in favour of binaries, which my first attempt tripped over. Now:

• 1 configuration file(s) validated

No deprecation warnings.

⚠️ This PR alone does not complete the migration

Two changes belong in patramsey/homebrew-tap, not here, and they're user-facing:

1. Add tap_migrations.json at the tap root:

   { "namecom": "namecom" }

2. Delete Formula/namecom.rb

Until both land, an existing brew install namecom keeps resolving the stale formula and never sees the cask. The migrations file is what makes brew upgrade follow the rename. I haven't touched the tap — that's a separate repo and affects anyone who has already installed, so it's your call when.

Sequencing that avoids a gap: merge this, then make the tap changes, then the next release publishes Casks/namecom.rb and existing users migrate on their next brew upgrade.

brew trust patramsey/tap in the README stays correct — brew trust covers "tap formulae, casks or commands".

Test plan

• goreleaser check — validates with zero deprecation warnings
• goreleaser release --snapshot --clean — cask generated successfully
• Generated cask contains on_linux blocks for amd64 and arm64
• Generated cask has no depends_on macos (the thing supports_linux? keys off)
• ruby -c on the generated cask: Syntax OK
• brew trust confirmed to be a real command covering casks
• Not verifiable until the next tag — release.yml only runs on tags