Installation scripts for Linux, Windows and MacOS

# Installation scripts for Linux, Windows and macOS ## Problem Currently there's no installation script for ponytail. Users need to manually clone the repository and handle dependencies themselves, which assumes some familiarity with git and OS-level tooling. ## Proposal Add install scripts for Linux, macOS, and Windows, so users (including beginners and those relying on AI coding agents) can install and start using ponytail's features without manual setup. ## Scope - `install.sh` for Linux/macOS - `install.ps1` for Windows - Detect dependencies and install them automatically (or report what's missing) - Document usage in README ## Why This lowers the barrier to entry, especially for non-technical users and AI coding agent workflows that benefit from a single setup command.