Function contributeSelectionCommands

Contribute the selection behavior onto contribution (a per-pane layer scope's contribution), as thin delegates to the layer's SelectionNavigation handle. Mirrors contributeClipboardCommands — a plain fn the wiring component calls, so the contributor is separately injectable. Returns a remover for parity with the other dynamic contributors; selection has no model listeners (pure delegation), so the commands themselves are torn down by the caller's contribution.remove().

The key inventory is the navigation's own binding map — no parallel key list to drift from it. Command CHROME (label / description / shortcut / tags) comes from the catalog (selection.cmd.json, scope selection); catalog keys with no binding here (and no sheet) stay chrome-only ⇒ disabled.