feat: add universal installation scripts for all platforms

[timimsms]

Summary

• Adds platform-specific installation scripts for easy one-line installation
• Provides a clean installation webpage for better user experience
• Updates README with quick install commands

What's Included

Installation Scripts

• scripts/install.sh: Unix installer (macOS/Linux)

  • Automatic platform/architecture detection
  • Support for multiple architectures (x86_64, arm64, i386, armv7)
  • Checksum verification
  • PATH configuration assistance
  • curl/wget fallback support

• scripts/install.ps1: Windows PowerShell installer

  • Architecture detection (x86_64, i386, arm64)
  • Windows-specific PATH management
  • Admin privilege detection
  • PowerShell completion setup instructions

Installation Webpage

• docs/install/index.html: User-friendly installation guide
  • Platform-specific tabs
  • Copy-to-clipboard functionality
  • Multiple installation methods
  • Clear instructions and troubleshooting

Features

Both scripts support:

• ✅ Version selection (--version v1.0.0)
• ✅ Custom installation directory
• ✅ Checksum verification for security
• ✅ Progress indicators
• ✅ Helpful error messages
• ✅ Automatic PATH configuration

Usage

Quick Install Commands

Unix (macOS/Linux):

curl -sSL https://raw.githubusercontent.com/timimsms/cu/main/scripts/install.sh | bash

Windows (PowerShell):

irm https://raw.githubusercontent.com/timimsms/cu/main/scripts/install.ps1 | iex

Installation Options

# Install specific version
curl -sSL [...] | bash -s -- --version v1.0.0

# Install to custom directory  
curl -sSL [...] | bash -s -- --dir /usr/local/bin

# Show help
curl -sSL [...] | bash -s -- --help

Testing

A test script is included to validate the installation scripts:

./scripts/test-install.sh

GitHub Pages Setup Required

After merging, you'll need to enable GitHub Pages:

1. Go to Settings → Pages
2. Source: Deploy from a branch
3. Branch: main
4. Folder: /docs
5. Save

The installation guide will be available at: https://timimsms.github.io/cu/install/

Security Considerations

• Scripts verify checksums before installation
• Users are encouraged to review scripts before running
• Clear warnings about PATH modifications
• No sudo required for default user installations

Next Steps

This completes the installation scripts feature. After merging:

• Enable GitHub Pages for the installation guide
• Test installation on various platforms
• Consider adding installation analytics (opt-in)

🤖 Generated with Claude Code

[timimsms]

Deprioritized. Homebrew and direct GitHub Release downloads (PR #17) cover the primary installation paths. Universal install scripts can be revisited if needed.