feat(neotree): +neotree/refresh to keep neotree in sync on buffer switches

[pmbittner]

This PR adds the new +neotree/refresh function that refreshes neotree to show the current buffer's file. By adding the following snippet to your config.el to run the refresh on every buffer switch, neotree is always up to date:

(after! neotree
  (add-hook 'doom-switch-buffer-hook #'+neotree/refresh))

The following screencast demonstrates the automatic synchonization by switching between buffers. Note that we do not refresh neotree when we visit a buffer that does not correspond to a file, such as *Messages* and *doom*.

Screencast.From.2026-02-08.17-49-04.webm

For now, the automatic synchronization of neotree is not enabled by default to not break existing behavior. Instead, I documented how to enable it in modules/ui/neotree/README.org.

(The commit messages are missing their scope (neotree) because the commit linter says it is an invalid scope. I'd be happy to change the commit messages if requested.)

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• I searched the issue tracker and this hasn't been PRed before.
• My changes are not on the do-not-PR list for this project.
• My commits conform to Doom's git conventions.
• I am blindly checking these off.
• This PR contains AI-generated work. (I drafted a first version of this code with ChatGPT. None of that code survived but it pushed me into the right direction.)
• Any relevant issues or PRs have been linked to.
• This a draft PR; I need more time to finish it.