Add a fabrik init workflow with templates for Rust, Elixir, Go, macOS CLI, and iOS apps

Fabrik now ships a built-in init workflow with declarative templates for scaffolding new projects. The first set of supported project types covers Rust libraries, Elixir projects, Go projects, macOS command-line tools, and iOS apps, so you can generate a working starting project from a single command instead of hand-wiring a fabrik setup.