[ISSUE #783] Move FAQ docs to stable top-level path with legacy redirect

[majialoong]

What is the purpose of the change

See #783

The FAQ page URL is currently tied to its location and ordering under the Best Practice docs. When the Best Practice document structure changes, the FAQ URL may change as well, which can break externally referenced links.

Since the FAQ URL may be printed by clients as user-facing guidance, it should use a stable public path.

Brief changelog

Use stable FAQ URLs to ensure that users can always access the correct page based on the URL.

Historically, /docs/faq/ has already been exposed publicly, so this PR uses it as the fixed FAQ URL instead of introducing a new /docs/FAQ path. The legacy /docs/bestPractice/06FAQ URL is kept as a redirect to /docs/faq/.

Verifying this change

Local test.

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