Lists duplicate, rename and edit values right in their rows

Name, opacity and Z each sat in a separate field below or beside
the list. You had to select a row first and then look elsewhere to
change it. Duplicating was a separate button or not possible at all.
Now the row itself carries everything.

- SortableList gets three optional callbacks. onDuplicate shows a
  copy button between the eye and the delete button. onRename opens
  a text field on double click, Enter or a click outside commits,
  Esc cancels, an empty name is ignored. value puts a NumberField
  into the row.
- Dragging on the number changes the value and never moves the row.
  A whole drag is one undo step, the canvas follows live.
- Copy and delete only show on the hovered and the selected row.
  Their space stays reserved, so nothing jumps on hover.
- Pixel layers: copy right above with the same pixels on all
  frames, rename, opacity in percent. The Name and Opacity fields
  below the list are gone.
- Pixel frames: copy right after, replaces the Duplicate button.
- Tilemap layers: copy with cells, Z and visibility, rename, Z in
  the row. The Name and Z fields in the panel are gone.
- Vector shapes: copy at the same place and select it, rename.
- New in core: DuplicateVectorShapeCommand,
  DuplicateTilemapLayerCommand, withLayerDuplicated and copyName
  ("X copy", "X copy 2"). copyName lives in src/core/util/names.ts
  because the model never imports from commands/.

Findings:

- Double clicking a shape that is not selected yet only selects it.
  The first click moves the list up, so the second click misses the
  name. Module 47 selects the row first.

Tests:

- ./check.sh: 138 files, 2055 tests, CHECK EXIT 0 (before 2052).
- GM_STEPS=47,48 (fresh, twice): ALL PASSED, 91 checks (before 86).
- GM_STEPS=39,40,47,48: module 40 green, 47 died on the rename
  check, which was a test fault and is fixed.
- Counter probes: a constant copyName fails the shape and pixel
  layer tests. A dead copy hit fails the copy check in 47.
- Check total 1272 in README and wiki, computed (1266 + 6).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/core/model/pixelEdit.ts

@@ -6,6 +6,7 @@
  * one that cannot do what is asked throws a `PixelEditError` with the reason in words.
  */
 import type { PixelArtAsset, PixelFrame, PixelLayer } from './Asset';
+import { copyName } from '../util/names';
 import { PIXEL_CANVAS_MAX } from './pixelCel';
 
 export interface PixelArtState {
@@ -83,6 +84,26 @@ export function withLayerAdded(state: PixelArtState, id: string, aboveId = ''):
   return next;
 }
 
+/**
+ * A copy of a layer right above it, named after it, with its cels on every frame. The cels are files
+ * named by their content, so the copy names the same files and costs no upload.
+ */
+export function withLayerDuplicated(state: PixelArtState, id: string, sourceId: string): PixelArtState {
+  const next = cloneState(state);
+  const index = layerIndex(next, sourceId);
+  const source = next.layers[index]!;
+  const name = copyName(
+    next.layers.map((layer) => layer.name),
+    source.name,
+  );
+  next.layers.splice(index + 1, 0, { ...source, id, name });
+  for (const frame of next.frames) {
+    const cel = frame.cels[sourceId];
+    if (cel) frame.cels[id] = cel;
+  }
+  return next;
+}
+
 /** Takes a layer out, with its cels on every frame. The last layer stays: there would be nothing to paint on. */
 export function withLayerRemoved(state: PixelArtState, layerId: string): PixelArtState {
   const next = cloneState(state);