docs(readme): lead with curl install.sh one-liner

Add `curl -fsSL https://runfusion.ai/install.sh | sh` as the primary
install path in both the root README and the CLI README (npm page).
The installer auto-detects Homebrew (then falls back to npm) so users
get a single command regardless of platform. Keep the explicit brew /
npm paths below for discoverability.

packages/cli/README.md

@@ -20,6 +20,14 @@
 
 ## Install
 
+**One-line install** (macOS & Linux):
+
+```bash
+curl -fsSL https://runfusion.ai/install.sh | sh
+```
+
+Picks Homebrew if available, falls back to npm.
+
 **Homebrew** (macOS & Linux):
 
 ```bash