Add --version flag to install scripts for pre-release testing

[aniongithub]

Summary

The install scripts (install.sh and install.ps1) always fetch the latest release. We need a --version flag so we can install a specific version — especially useful for testing pre-release builds without making them the \latest.

Details

• install.sh: add --version CLI arg (e.g. curl ... | bash -s -- --version v0.36-rc1)
• install.ps1: add -Version parameter
• When specified, skip the GitHub API latest-release lookup and download directly from the given tag
• When omitted, keep the current behavior (fetch latest)