Publish flux CLI to Homebrew on release

[JoeriDijkstra]

Goal

Install the flux CLI with Homebrew

Install the flux CLI with brew install eyra/tap/flux-cli and keep it current through brew upgrade.

Changes

• GoReleaser homebrew_casks publishes Casks/flux-cli.rb to eyra/homebrew-tap on every tagged release, over SSH with a write deploy key (HOMEBREW_TAP_DEPLOY_KEY secret, already set).
• The cask's postflight strips com.apple.quarantine. Without it, Gatekeeper kills the unsigned binary (exit 137).
• The cask is named flux-cli because flux collides with the f.lux cask and the fluxcd formula. The installed binary is still flux.
• The deploy key is read with index .Env, so the secret-less snapshot step still passes.
• README documents the brew install.

Verification

• goreleaser check passes.
• goreleaser release --snapshot --clean passes without the secret, writes dist/homebrew/Casks/flux-cli.rb, and leaves the tree clean.
• brew install eyra/tap/flux-cli (tap seeded with v0.2.1) installs and runs flux --help; quarantine is removed.