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/core/store/serialize.ts

@@ -194,13 +194,21 @@ function normalizeStructFields(raw: unknown): StructFieldDef[] {
     const f = asRecord(item);
     const key = typeof f.key === 'string' ? f.key : '';
     if (!/^[A-Za-z_][A-Za-z0-9_]*$/.test(key) || seen.has(key)) continue;
-    if (!(FIELD_KINDS as readonly string[]).includes(String(f.kind))) continue;
+    const field = readField(key, f);
+    if (!field) continue;
     seen.add(key);
-    fields.push({ key, kind: f.kind as FieldKind });
+    fields.push(field);
   }
   return fields;
 }
 
+function readField(key: string, f: Record<string, unknown>): StructFieldDef | null {
+  const isFieldKind = (value: unknown) => (FIELD_KINDS as readonly string[]).includes(String(value));
+  if (f.kind === 'list')
+    return { key, kind: 'list', items: isFieldKind(f.items) ? (f.items as FieldKind) : 'number' };
+  return isFieldKind(f.kind) ? { key, kind: f.kind as FieldKind } : null;
+}
+
 function normalizePorts(raw: unknown): DeclaredPort[] {
   const ports: DeclaredPort[] = [];
   const seen = new Set<string>();