docs(ospo): add make test-acceptance-webui per phil-davis review

Apply suggestion from #41567 (comment)
Signed-off-by: David Walter <david.walter@kiteworks.com>

Author: dj4oC

agents.md

@@ -53,6 +53,9 @@ make test-acceptance-api
 # Test (acceptance - CLI)
 make test-acceptance-cli
 
+# Test (acceptance - Web User Interface)
+make test-acceptance-webui
+
 # Lint (PHP)
 make test-php-style