Part of #2422: a selected clip group shows its clipping path's outline, not its hidden art

A selected clip group drew the outline of everything inside it: the
clipping path, the whole rectangle of a clipped image, and the whole
outline and anchors of each clipped path. The Selection tool's
bounding box, which fits the clipping path, showed on top of them.
The hover highlight and the key object outline drew the same hidden
art.

The selection overlay, the hover highlight and the key object outline
now show only the clipping path of a clip group or clipping layer,
its first child. The overlay's limit on anchors counts only that path
too, so a clip group that hides a large trace still shows its
clipping path's anchors and hover highlight. The art inside still
shows its whole outline when it is selected on its own: with Edit
Contents, a Direct or Group Selection click, or in isolation mode.

Docs: docs/target-app-parity.md.

docs/target-app-parity.md

@@ -495,6 +495,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
     Align and Distribute Spacing keep a compound path or selected group that contains the key object in place, as they keep the key object itself.
     Anchor Align moves the selected points to their bounds or the artboard (#1180). Repeating it, or moving by at most 1e-9 pt on both axes as whole-object Align does, leaves the document, Undo, Redo and saved state unchanged; actual moves still take one undo step. `crates/engine/src/tests.rs` covers repeated alignment, rounding-only alignment, unchanged handles, saved state, command recording and Undo/Redo.
     A symbol instance is measured by its symbol's art, as its transform places it, for clicks, the marquee, the bounding box, the Transform panel, Align and Distribute (the art's strokes too with Use Preview Bounds), Fit to Artwork Bounds, exports of the art, thumbnails and canvas culling; one whose symbol is missing is measured as the 20 × 20 square around the origin.
+    A selected clip group shows the outline and anchors of its clipping path, not of the art the path clips, and its hover highlight and key object outline follow the clipping path too. That art shows its whole outline when it is selected on its own: with Edit Contents, Direct or Group Selection, or in isolation mode (#2422).
     Clear deletes individual selected compound-path members without deleting their siblings, and explicit object ids work without a selection; Cut still removes the same objects it copies (#786).
     A command that leaves out an object selected inside a selected group also leaves it out when `ids` list it together with a group that holds it. Make Repeat and Live Paint no longer fail on such a list, New Symbol no longer stores the object twice, and `object.transform` no longer moves it twice.
   - **Compound paths:** Make keeps the backmost object's appearance and each contour; selecting a member in Direct Selection reads and changes the compound's fill rule in Attributes. Direction remains a per-member edit. Rendered holes, unchanged contour geometry, no-op history and Undo/Redo are covered by `engine/tests/compound_attributes.rs` (#1197). Behaviour reference: [public compound-path documentation](https://helpx.adobe.com/illustrator/desktop/manage-objects/reshape-transform-objects/create-compound-paths.html). Make Compound Path on a group (such as outlined type) keeps the paint of its backmost path instead of drawing nothing, and compound paths joined into one keep their holes (#1537).