* Create user_agent_auth.md
Adding documentation for agent authentication on behalf of a user
* Update user_agent_auth.md
* Rename user_agent_auth.md to user-agent-auth.md
* break content out to separate guides
* add links/overview
* edits
* fix sentence
* Fix broken links
* Fix: Change 'get_user_config' fn name to 'my_node'
* Fix: Add reference to custom auth in MCP docs example
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Co-authored-by: Lauren Hirata Singh <lauren@langchain.dev>
Manual pass to apply a few heuristics:
* Boost conceptual pages
* Deboost (is that a word?) index pages that list all content
* Prefer Agents pages if search query contains the word "agent"
* Add tags for a few selected pages