Document all supported installation methods

[anujmindfire]

Create comprehensive installation documentation covering every supported installation method.

Sections
GitHub Releases
Go Install
npm
Homebrew
curl installer
PowerShell installer
Verify installation
Upgrade
Uninstall
Troubleshooting
Platform compatibility

Acceptance Criteria

Every installation method has:
Installation steps
Upgrade instructions
Uninstall instructions
Troubleshooting guidance