fix(release): repair Homebrew formula packaging

[phall1]

Summary

• emit a stable top-level Homebrew formula URL/sha256 while keeping platform-specific overrides for other artifacts
• build macOS release artifacts with rustup + setup-zig instead of nix develop
• add a macOS otool guard against /nix/store dylib load commands before packaging
• add scripts/check-formula.sh and wire it into just ci

Validation

• bash scripts/check-formula.sh
• bash -n scripts/gen-formula.sh scripts/check-formula.sh scripts/dist.sh scripts/install.sh
• shellcheck scripts/gen-formula.sh scripts/check-formula.sh scripts/dist.sh scripts/install.sh
• just formula-check
• just docs-check
• ruby YAML parse for .github/workflows/release.yml
• git diff --check

Notes

The currently published v0.0.2 arm64 macOS artifact links /nix/store/.../libiconv.2.dylib. This PR prevents publishing that shape again, but the tap/artifacts need a release rerun after merge.

Fixes phux-alcc.

Co-Authored-By: Warp agent@warp.dev