docs: simplify quickstart to npx onboard, mention create-adapter skill

- Remove Docker option from quickstart, make `npx paperclipai onboard --yes` the recommended path
- Add tip about `create-agent-adapter` skill in the creating-an-adapter guide

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/adapters/creating-an-adapter.md

@@ -5,6 +5,10 @@ summary: Guide to building a custom adapter
 
 Build a custom adapter to connect Paperclip to any agent runtime.
 
+<Tip>
+If you're using Claude Code, the `create-agent-adapter` skill can guide you through the full adapter creation process interactively. Just ask Claude to create a new adapter and it will walk you through each step.
+</Tip>
+
 ## Package Structure
 
 ```