M4.23: paste placement, Paste Remembers Layers and the Paste menu's enable rule

Paste (also without formatting) goes to the centre of the view
(edit.paste {center}); Paste in Front/Back with nothing selected go to
the top/bottom of the current layer, in order; Paste on All Artboards
keeps the objects' offset to the artboard they were copied from.
layer.pasteRemembersLayers {on?} (document flag paste_remembers_layers,
saved, document.inspect) pastes objects back into the layers they came
from by name, making missing ones; the Layers panel now has its menu
with the layer commands and the check item. The Paste menu items are
enabled while the system clipboard holds SVG (looked at once per frame
at most, a few times a second).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/control-protocol.md

@@ -233,3 +233,9 @@ dialog instead and answers `{dialog: "swatchConflict"}`. Fields: `conflicts` (`[
 spot}]`), `index` (the conflict asked about), `choice` (`merge` or `add`), `applyToAll` and `choices` (the answers so
 far). `ui.dialog.confirm` records the answer and asks about the next conflict (with `applyToAll`, answers the rest
 the same); the last one runs the paste with `swatchConflict`. `ui.dialog.cancel` pastes nothing.
+
+Paste placement: through the app, `edit.paste` and `edit.pasteWithoutFormatting` without `center`, `dx` or `dy`
+paste at the centre of the view. The Paste menu items are enabled while the system clipboard holds SVG, even with
+nothing copied in the app (looked at up to four times a second; `ui.menu.list` shows it). The Layers panel menu (≡ on
+the dock's tab strip while Layers shows) lists the layer commands and Paste Remembers Layers
+(`layer.pasteRemembersLayers`, checked when on).