The event also fires on deselection and now carries a set of entities
rather than a single one, so the "SelectionChanged" name (matching
SelectionChangedEvent and ScrapSelectionChangedEvent) is more accurate.
Pure rename: header + include guard, CMake entry, and all usages.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Y7N59FsLA5e2kuVdqe4Uhc
