Duplicate chat plugin created by smoke

[evanklem]

Describe the bug

The chat plugin ships as a built-in under plugins/chat/, but an identical copy was also committed to .polypore/plugins/polypore.chat/.

The .polypore/plugins/ directory is meant only for user-installed plugins. As noted in plugin_store.rs:

Each installed plugin lives at <project>/.polypore/plugins/<id>/

Built-ins are bundled, not installed, so the registry copy is redundant and produces a duplicate polypore.chat plugin ID.

To reproduce

1. Start from a clean working tree.

2. Inspect the plugin directories.

3. Observe that the chat plugin exists in both locations:

   • plugins/chat/
   • .polypore/plugins/polypore.chat/

4. Run plugin discovery or start the app.

5. Observe that polypore.chat is discovered twice: once as a built-in and once as an installed plugin.

Expected behavior

The chat plugin should only be bundled as a built-in under plugins/chat/.

The .polypore/plugins/ registry should contain only user-installed plugins, so polypore.chat should not appear there unless the user explicitly installed it.

Actual behavior

An identical copy of the built-in chat plugin exists under .polypore/plugins/polypore.chat/, causing a duplicate polypore.chat plugin ID.

Suggested fix

Remove .polypore/plugins/polypore.chat/ from the repository and keep the chat plugin only under plugins/chat/.

If needed, also add a guard to prevent bundled built-ins from being written into the user-installed plugin registry.