Homebrew tap for `brew install riskkernel`

[prashar32]

Make brew install riskkernel a one-liner on macOS/Linux — a common install path that lowers friction.

Scope: a Homebrew formula (a tap repo, or goreleaser's brew integration) that installs the released riskkernel binary from the GitHub release artifacts, wired into the release flow so each tag updates the formula.

Acceptance: brew install …/riskkernel installs a working binary matching the latest release; the formula updates on release. The release already publishes signed binaries via goreleaser — this rides on those.