Finish the struct and list leftovers: inline lists, list fields, item kinds

An unconnected list input is a button into the List tab instead of a number
field; a struct field can hold a list, so ListSlot carries an optional field
name and the three owner cases only say what sits at a key; and a list
variable picks its item kind in the inspector (marker doubles as the chooser),
so a list of structs no longer has to be born from a project file.

The declaration keeps the storable shapes finite: a struct field may be a list,
but that list holds primitives only, so list->struct->primitive and
struct->list->primitive are the two deepest forms.

check 674, e2e 483, jump-run 24, Tetris 19.

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

src/editor/inspector/objectSection.ts

@@ -320,7 +320,13 @@ function propertyRow(
     {
       ...previewingHandlers<ObjectRef>(host, overrideSpec),
       ...listOpener(host.state, def, () => ({ kind: 'object', holderId, objectId, key: def.key })),
-      ...structFields<ObjectRef>(host, def, overrideSpec),
+      ...structFields<ObjectRef>(host, def, overrideSpec, (field) => ({
+        kind: 'object',
+        holderId,
+        objectId,
+        key: def.key,
+        field,
+      })),
     },
     {
       extra: aspectActions(