feat(antigravity): prefer prod URL as first priority

Promote cloudcode-pa.googleapis.com to the first position in the
fallback order, with daily and sandbox URLs as fallbacks.

internal/runtime/executor/antigravity_executor.go

@@ -2270,9 +2270,9 @@ var antigravityBaseURLFallbackOrder = func(auth *cliproxyauth.Auth) []string {
 		return []string{base}
 	}
 	return []string{
+		antigravityBaseURLProd,
 		antigravityBaseURLDaily,
 		antigravitySandboxBaseURLDaily,
-		// antigravityBaseURLProd,
 	}
 }