Expose hosted plugin extensions in app-server summaries

[copyberry]

Expose hosted plugin extensions in app-server summaries

What changed

• Request installed-plugin metadata with includeExtensions=true and carry optional extensions through the cache into PluginSummary.
• Add typed declarations for global, settings, thread, and file entrypoints, quick actions, settings tools, icons, and search mention providers. Update JSON schemas and TypeScript and Python bindings.
• Accept supported snake_case aliases and emit camelCase fields. Discard incompatible extension declarations without invalidating the installed-plugin inventory.

Testing

Add an integration test covering extension metadata preservation, field normalization, and unknown entrypoint and quick-action types across live and cached plugin/installed reads. Update pagination assertions to require includeExtensions=true.

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