Offer to Install Coder CLI

### Problem Description

Coder Desktop does not install or expose the CLI, requiring manual installation that creates friction for users as they need to keep the CLI up to date separately.

### Desired Solution

Coder Desktop should:

* Detect and install the correct CLI version if missing or outdated
* Expose the CLI via a symlink in a standard location (e.g., `/usr/local/bin`), similar to how Tailscale handles it