feat(release): build native macOS installers

[nkavian]

Summary

• build macOS release artifacts on native arm64 and x64 runners
• render a multi-architecture Homebrew Cask from separate checksums
• point install and update messaging at https://inflowcli.ai/ instead of npm-specific commands

Verification

• pnpm typecheck
• pnpm lint
• pnpm test
• pnpm typedoc
• pnpm build
• pnpm format:check
• workflow YAML parse check
• local arm64 macOS app package build with ad hoc signing
• multi-architecture Homebrew Cask render with dummy artifacts and ruby -c

Notes

• Hosted install.sh/install.ps1 live in inflow-server and need a separate repo change.
• The attempted dry-run was canceled because the validation branch used an unwanted codex-prefixed name.
• Real notarized release remains parked until Apple notarization is behaving normally.

[nkavian]

Closing to recreate from feat/native-macos-installers.