chore: add shared and frontend skills

.agents/skills/playwright/NOTICE.txt

@@ -0,0 +1,14 @@
+This skill includes material derived from the Microsoft playwright-cli repository.
+
+Source:
+- Repository: microsoft/playwright-cli
+- Path: skills/playwright-cli/SKILL.md
+
+Copyright (c) Microsoft Corporation.
+
+Licensed under the Apache License, Version 2.0.
+See LICENSE.txt in this directory.
+
+Modifications:
+- Adapted for the Codex skill collection.
+- Added a wrapper script and local reference guides.