feat(bt)!: Remove legacy tree definition format

The `LegacyTreeDef` type and its normalization path have been removed.
All tree definitions must now use the factory functions (`leaf`,
`sequential`, `parallel`, `selector`, `random`, `repeat`). The
`TreeDef` type is now simply `TaskEntityDef`.

examples/blackjack/main.ts

@@ -23,7 +23,13 @@
 //   npx tsx examples/blackjack/main.ts
 
 import { World } from "../../src/index";
-import { buildTree } from "../../src/bt/index";
+import {
+  buildTree,
+  leaf,
+  parallel,
+  repeat,
+  sequential,
+} from "../../src/bt/index";
 import { CommandQueue } from "../../src/commands/index";
 
 import {
@@ -63,50 +69,37 @@ const commands = new CommandQueue(world);
 registerCommands(world, commands, cards);
 
 // ── Behaviour Tree ───────────────────────────────────
-const runner = buildTree(world, {
-  kind: "parallel",
-  children: [
-    {
-      kind: "leaf",
-      *run() {
-        while (true) {
-          const dt: number = yield;
-          const phase = world.getSingleton(GamePhase);
-          if (phase.phase !== "dealerTurn") continue;
+const runner = buildTree(
+  world,
+  parallel([
+    leaf(function* dealerPlay() {
+      while (true) {
+        yield;
+        const phase = world.getSingleton(GamePhase);
+        if (phase.phase !== "dealerTurn") continue;
 
-          if (dealerShouldHit(cards.getHand(InDealerHand))) {
-            const cardEntity = cards.drawCard();
-            if (cardEntity) {
-              cards.dealTo(cardEntity, InDealerHand);
-            }
-          } else {
-            resolveRound(world, cards);
+        if (dealerShouldHit(cards.getHand(InDealerHand))) {
+          const cardEntity = cards.drawCard();
+          if (cardEntity) {
+            cards.dealTo(cardEntity, InDealerHand);
           }
+        } else {
+          resolveRound(world, cards);
         }
-      },
-    },
-    {
-      kind: "repeat",
-      child: {
-        kind: "sequential",
-        children: [
-          {
-            kind: "leaf",
-            run: () => {
-              commands.execute();
-            },
-          },
-          {
-            kind: "leaf",
-            run: () => {
-              render(world, ui);
-            },
-          },
-        ],
-      },
-    },
-  ],
-});
+      }
+    }),
+    repeat(
+      sequential([
+        leaf(() => {
+          commands.execute();
+        }),
+        leaf(() => {
+          render(world, ui);
+        }),
+      ]),
+    ),
+  ]),
+);
 
 // ── Input → Command mapping ──────────────────────────
 const keyToCommand: Partial<Record<Key, typeof Hit>> = {