feat(bt): Add entity-based task factories

Add `leaf`, `sequential`, `parallel`, `selector`, `random`, and `repeat`
functions that return `EntityDef` trees. Legacy object definitions are
still
accepted for backward compatibility. Non-task child entities are ignored
by
the runner, and `buildTree` now stores the root entity on
`TaskRunner.root`.

test/bt.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect, beforeEach } from "vitest";
-import { World, type Entity } from "../src/index";
+import { World, defineComponent, entity, type Entity } from "../src/index";
 import {
   Task,
   Scheduled,
@@ -9,6 +9,10 @@ import {
   Cancelled,
   ChildOf,
   TaskRunner,
+  buildTree,
+  leaf,
+  repeat,
+  sequential,
 } from "../src/bt/index";
 
 // ── Helpers ─────────────────────────────────────────
@@ -54,6 +58,60 @@ function makeSelector(world: World, parent?: Entity): Entity {
   return e;
 }
 
+// ── Entity task factories ───────────────────────────
+describe("Entity task factories", () => {
+  it("materializes non-task child entities and ignores them during execution", () => {
+    const Label = defineComponent("testLabel", { value: "" });
+    const world = new World();
+    const calls: string[] = [];
+
+    const runner = buildTree(
+      world,
+      sequential([
+        entity(Label, { value: "sequence metadata" }),
+        leaf(() => calls.push("a")),
+        entity(Label, { value: "between leaves" }),
+        leaf(() => calls.push("b")),
+      ]),
+    );
+
+    const root = runner.root!;
+    const children = [...world.getRelatedTo(root, ChildOf)];
+    const labels = children
+      .filter((child) => world.has(child, Label))
+      .map((child) => world.get(child, Label).value);
+
+    expect(labels).toEqual(["sequence metadata", "between leaves"]);
+
+    runner.schedule(root);
+    for (let i = 0; i < 5; i++) runner.tick();
+
+    expect(calls).toEqual(["a", "b"]);
+    expect(world.has(root, Succeeded)).toBe(true);
+  });
+
+  it("repeat works with component child entities beside its task child", () => {
+    const Label = defineComponent("repeatLabel", { value: "" });
+    const world = new World();
+    let calls = 0;
+
+    const runner = buildTree(
+      world,
+      repeat([
+        entity(Label, { value: "repeat metadata" }),
+        leaf(() => {
+          calls++;
+        }),
+      ]),
+    );
+
+    runner.schedule(runner.root!);
+    for (let i = 0; i < 5; i++) runner.tick();
+
+    expect(calls).toBeGreaterThan(1);
+  });
+});
+
 // ── Leaf tasks ──────────────────────────────────────
 describe("Leaf tasks", () => {
   let world: World;