docs: pin Antigravity registry check to 2.2.3

docs/ANTIGRAVITY-GUIDE.md

@@ -14,7 +14,7 @@ Verify that 2.2.3 is readable from the registry, then run the pinned package
 from the project you want to configure:
 
 ```bash
-npm view ecc-universal version
+npm view ecc-universal@2.2.3 version
 npx ecc-universal@2.2.3 install --profile minimal --target antigravity
 ```