[Feature] Additional Installation Methods

[michaelmcnees]

Problem

Make installation easier for anyone, even without Go.

Proposed solution

Add distribution to our pipelines for homebrew and explore other options for popular package repos.

[michaelmcnees]

Shipping a private Homebrew tap for v0.6.0 — the viable path given Mantle's BSL license (homebrew-core requires OSI-approved licenses, which BSL is not).

What shipped:

• Created dvflw/homebrew-mantle tap repo
• goreleaser brews: stanza in .goreleaser.yaml — auto-generates and pushes Formula/mantle.rb on every stable release
• Release workflow updated to pass HOMEBREW_TAP_TOKEN

One manual step required: Create a fine-grained PAT with Contents: read+write on dvflw/homebrew-mantle and store it as secret HOMEBREW_TAP_TOKEN on this repo.

User install:

brew tap dvflw/mantle
brew install mantle

Closes #11