[Feature] squad upgrade --self to update the CLI package #801

Self-Upgrade

Users should be able to update the Squad CLI itself from within squad, not just repo files.

Usage

• squad upgrade --self — install latest stable
• squad upgrade --self --insider — install latest insider/prerelease
• After installing, automatically runs repo upgrade to apply new templates

Why

Currently users must manually run npm install -g @bradygaster/squad-cli@latest to get the latest CLI. This should be a single command.