Metadatasource cleanup docs

[semohr]

This PR includes documentation updates for the new metadatasource plugin architecture, as requested by @snejus. The docs changes were split out from the original implementation to keep things focused and reviewable.

• Introduces comprehensive documentation for the new metadata plugin system.
• Performs a general cleanup of the plugin-related developer documentation for clarity and consistency.

To review this, you may want to checkout the PR branch and have a look at the docs locally.

gh pr checkout 5861
cd docs
make html

Note:
This PR should be reviewed and merged together with [#5787]

[Copilot]

Pull Request Overview

Documentation for the new metadatasource plugin architecture has been added and the legacy monolithic plugin guide has been split into focused sections.

• Introduces separate “commands,” “events,” and “other” plugin dev guides under docs/dev/plugins/.
• Cleans up cross-references and landing pages, including updates to docs/plugins/index.rst and docs/dev/index.rst.
• Updates API docs (docs/api/plugins.rst) to include new metadata plugin classes.

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
docs/plugins/index.rst	Updated link to point at the new plugin dev index
docs/dev/plugins/other.rst	Added “Extending the Autotagger” guide
docs/dev/plugins/index.rst	Created plugin development index with toctree
docs/dev/plugins/events.rst	Added event-listener documentation
docs/dev/plugins/commands.rst	Added CLI subcommand guide
docs/dev/plugins.rst	Removed outdated monolithic plugin dev guide
docs/dev/index.rst	Added Confuse link and updated plugin toctree path
docs/api/plugins.rst	Added metadata plugin classes to API autosummary

Comments suppressed due to low confidence (1)

docs/dev/plugins/other.rst:111

• Remove the extra backtick after the Sphinx reference. It should close as :py:meth:beets.plugins.BeetsPlugin.add_media_field() method.

your plugins :py:meth:`beets.plugins.BeetsPlugin.add_media_field()`` method.

[semohr]

@beetbox/maintainers Could we get a review here please?
I split it out from #5787, but it's still very closely related. We're currently missing documentation for the new features, so this helps address that. 😉

[wisp3rwind]

Could you briefly point out which sections of the docs have actual changes to their content, and not just layout tweaks? Since the first commit moves around a lot of text, but also makes some changes to them, this is a little tricky to review. Thanks!

[snejus]

@semohr note you can just run poe docs from the repo root - no need for cd docs && make docs

[semohr]

Could you briefly point out which sections of the docs have actual changes to their content, and not just layout tweaks? Since the first commit moves around a lot of text, but also makes some changes to them, this is a little tricky to review. Thanks!

You're right, the first commit does move a lot of content around, which makes it tricky to spot the actual content changes. As far as I can tell, the only completely new section is the Extending the Autotagger section in other.rst.

If you'd prefer, I can split the structural changes and the content edits into separate commits for easier review. That might take a bit of time though, and since this is just developer docs, I figured a single pass might be sufficient. Let me know what works best for you!