docs: fix stale ecc-universal version pin in ANTIGRAVITY-GUIDE

The Quick Start section pinned ecc-universal@2.2.0 while every other
reference in the repo (README.md, and all other docs) uses @2.2.3.
This caused Antigravity users to install an outdated version.

Update the pin to @2.2.3 to match the rest of the codebase.

(cherry picked from commit a052b208e5)

docs/ANTIGRAVITY-GUIDE.md

@@ -15,7 +15,7 @@ from the project you want to configure:
 
 ```bash
 npm view ecc-universal version
-npx ecc-universal@2.2.0 install --profile minimal --target antigravity
+npx ecc-universal@2.2.3 install --profile minimal --target antigravity
 ```
 
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