feat(studio): element groups — studio UI (#1759)

* feat(studio): element groups — source mutations

Wrap/unwrap source mutations (group geometry, the wrap-elements / unwrap-elements
routes) that the studio group feature is built on. Studio UI lands in the next PR.

* fix(studio): hoverable group interior + non-sticky drill-in

Two group selection bugs with animated members:

1) Empty space inside a group's overlay didn't hover/select the group. Members
   animated outside the wrapper's static box (110px box vs 340px member union),
   so elementsFromPoint hit only the full-bleed background there. Add a
   member-union hit-test fallback: a point inside a group's live member bounds
   resolves to that group (innermost wins).

2) After drilling into a group and selecting a child, nothing else was
   selectable — out-of-scope resolved to null. Make drill-in non-sticky:
   interacting outside the drilled group re-resolves normally and exits the
   drill-in, so a later click on the group selects it as a unit again.

packages/studio/src/components/editor/DomEditOverlay.tsx

@@ -3,7 +3,7 @@ import { useMountEffect } from "../../hooks/useMountEffect";
 import { type DomEditSelection } from "./domEditing";
 import { useMarqueeGestures } from "./marqueeCommit";
 import { MarqueeOverlay } from "./MarqueeOverlay";
-import { resolveDomEditGroupOverlayRect, toOverlayRect } from "./domEditOverlayGeometry";
+import { groupAwareOverlayRect, resolveDomEditGroupOverlayRect } from "./domEditOverlayGeometry";
 import { collectDomEditLayerItems } from "./domEditingLayers";
 import { isElementComputedVisible } from "./domEditingElement";
 import {
@@ -248,7 +248,10 @@ export const DomEditOverlay = memo(function DomEditOverlay({
     const elMap = new Map<string, HTMLElement>();
     for (const item of items) {
       if (!isElementComputedVisible(item.element)) continue;
-      const r = toOverlayRect(overlay, iframe, item.element);
+      // Groups use their members' union (where they actually render), so a group
+      // whose members sit inside the canvas isn't flagged off-canvas by a stale
+      // wrapper box.
+      const r = groupAwareOverlayRect(overlay, iframe, item.element);
       if (!r) continue;
       // Any edge crossing the composition border → gray-zone indicator (the
       // in-canvas portion is clipped away below, so only the sliver shows).