feat(plugin): let server plugins emit custom bus events

[acramsay]

Issue for this PR

Partial implementation of #6330

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Add event.emit(type, properties) to PluginInput, publishing arbitrary namespaced event types (e.g. plugin..) on the Bus so clients can subscribe.

TUI plugins subscribe with api.event.on(...)

How did you verify your code works?

Screenshots / recordings

If this is a UI change, please include a screenshot or recording.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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[github-actions]

This PR doesn't fully meet our contributing guidelines and PR template.

What needs to be fixed:

• "How did you verify your code works?" section is empty. Please explain how you tested.
• Not all checklist items are checked. Please confirm you have tested locally and have not included unrelated changes.

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[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found one potentially related PR:

feat(plugin): add typed rpc and custom events (#46105)

This PR appears to be closely related as it also addresses custom events functionality for plugins. Both PRs deal with extending plugin capabilities to handle custom events, though PR #46105 mentions "typed rpc and custom events" while the current PR (#46186) specifically focuses on server plugins emitting custom bus events. These may be addressing overlapping concerns or the same feature from different angles.

[github-actions]

This pull request has been automatically closed because it was not updated to meet our contributing guidelines within the 2-hour window.

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