Add install script for one-command setup

[munezaclovis]

Summary

• Adds install.sh — a curl-pipe installer so users can set up pv with a single command:

  curl -fsSL https://pv.prvious.dev/install | bash
  

• Downloads the pv binary to /usr/local/bin, then runs pv install to bootstrap the full environment (PHP, FrankenPHP, Composer, Mago, DNS, HTTPS certs)

Features

• Progress bar with ■/･ characters in purple
• Rosetta detection — catches x86 shells running on ARM Macs
• Version pinning — --version 0.2.0 to install a specific release
• PHP version passthrough — --php 8.4 forwarded to pv install
• Auto PATH setup — detects zsh/bash/fish, writes to the correct config file, deduplicates
• Idempotent — safe to run twice, detects existing installations
• --no-modify-path — for CI environments
• GitHub Actions support — writes to $GITHUB_PATH
• Clean error messages on download failure (not raw curl output)

What it delegates

The script does NOT duplicate any PHP/FrankenPHP/Composer/Mago/DNS/cert logic. It only gets the pv binary in place and runs pv install --force, which already handles all of that with its own step-by-step output.

Prerequisites

This script expects release assets named pv-darwin-arm64 and pv-darwin-amd64 on GitHub releases. A release workflow for the Go binary is needed before this script is functional.