Document workspace switching in langsmith

[Florence Morris (fjmorris)]

Description

This update adds a direct FAQ answer for switching workspaces in the LangSmith UI so users can quickly find the navigation path without relying on external support responses.

Changes made:

• Added a new FAQ entry to src/langsmith/faq.mdx: "In LangSmith, how do I change my workspace?"
• Documented the UI flow: use the bottom-left profile/workspace picker, open the Organizations drawer, and choose a workspace from the dropdown.
• Added role-based clarification that Organization Admins can access all org workspaces, while other roles may be limited.

Resolves DOC-829.

Test Plan

• Verify the new FAQ entry appears on the LangSmith FAQ page with correct formatting.
• Confirm the instructions match current LangSmith UI behavior for workspace switching.
• Run make format and make lint (repo currently reports pre-existing lint violations outside this change).

Preview

https://langchain-5e9cc07a-preview-opensw-1772648257-7d84c9f.mintlify.app/langsmith/faq#in-langsmith-how-do-i-change-my-workspace

[github-actions]

Mintlify preview ID generated: preview-opensw-1772648257-7d84c9f

[Florence Morris (fjmorris)]

Closing PR because the information already exists in this section:
https://localhost:3000/langsmith/set-up-hierarchy#manage-and-navigate-workspaces