New assets could only be added through the + button. A right-click on a category heading or on the empty space below the rows now opens the same menu at the pointer. - ListView gets the callback onListMenu. It fires on a right-click on empty space or on a heading. Only the asset panel has headings, so other lists are not affected. - AssetPanel opens its + menu from there. - A right-click on a heading does not fold or unfold the category. A right-click on empty space clears the selection like a left-click. - A right-click on an asset still opens the menu of that asset. - The empty list now says "No assets - press + or right-click". Tests: - ./check.sh: 178 files, 2573 tests, CHECK EXIT 0 - e2e 1-4: ALL PASSED, 134 checks - 3 new checks in e2e 04 with real right-clicks: menu on the "Scenes" heading (21 types, heading stays folded), menu on empty space, and "Behavior" from that menu creates one, undone again. - Counter-probe: without the menu both right-click checks fail. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>