`nbdev_preview` uses doclinks to local server

Currently, docs rendered locally with nbdev_preview have doclinks to nbdev.fast.ai instead of localhost

Start by locating the nbdev_preview entry point and tracing how doclinks are generated for locally rendered documentation. Reproduce the issue with a local server and verify that the generated links use localhost rather than nbdev.fast.ai.

索引モデルが issue の本文から書いたものです。