Let a variable hold a list

A variable could only be a number, a text or a yes/no, so every set of values had
to be smuggled through a string - which is where Tetris got its unreadable
"03066326048763714" colours from. A list is now a value of its own, with an item
kind (number, text, yes/no, colour) that decides how the inspector reads the one
comma-separated line it is typed as, and eight nodes to work with: List, Fill,
Count, Item at, Set item, Sub list, Join lists, Index of.

Two traps came with it. An array is typeof 'object', so every place that told a
value from an entity had to learn the difference, or a list would have been
passed around as a game object. And a value was compared by identity in three
places - with lists that marks everything as an overridden property after each
reload, so those comparisons now compare contents.

There is no list of objects: a list is written to the project file and an object
is a live handle that no reload survives. A set of objects stays a list of names.

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

tools/lib/builders.mjs

@@ -46,5 +46,11 @@ export const node = (id, type, x, y, params = {}, ports) => ({
 /** A port a behavior's start or end node declares. */
 export const port = (key, kind) => ({ key, kind });
 
-/** A behavior variable declaration. */
-export const variable = (key, kind, value) => ({ key, label: key, kind, default: value });
+/** A behavior variable declaration. `items` is the item kind of a `list`, ignored otherwise. */
+export const variable = (key, kind, value, items) => ({
+  key,
+  label: key,
+  kind,
+  default: value,
+  ...(items ? { items } : {}),
+});