fix: add codex skill metadata for gstack skills (#339)

.agents/skills/gstack-setup-browser-cookies/agents/openai.yaml

@@ -0,0 +1,6 @@
+interface:
+  display_name: "gstack-setup-browser-cookies"
+  short_description: "Import cookies from your real browser (Comet, Chrome, Arc, Brave, Edge) into the headless browse session. Opens an..."
+  default_prompt: "Use gstack-setup-browser-cookies for this task."
+policy:
+  allow_implicit_invocation: true