feat: implement full Root.unmount() with disposeFiber and instance cleanup

src/host/config.ts

@@ -2,6 +2,7 @@ import type { UNode, UElement, URoot, ComponentFn, UComponent } from "../core/sc
 import { isURoot, isUPrimitive } from "../core/schema.js";
 import { Context } from "../core/context.js";
 import type { Fiber } from "./fiber.js";
+import { disposeFiber } from "./fiber.js";
 import { reconcileProps, reconcileChildren, commitMutations } from "./reconcile.js";
 import type { CommitContext } from "./reconcile.js";
 
@@ -302,8 +303,18 @@ export function createRoot<TTag extends string, Instance, RootCtx>(
       host.emit?.("root.render", `root_${Date.now()}`, { childCount: payloadChildren.length });
     },
     unmount() {
+      const rootFiber = this.rootFiber;
+      if (!rootFiber) return;
+
+      disposeFiber(rootFiber, host as import("./fiber.js").HostLike<Instance, RootCtx>, ctx);
+
+      for (const child of rootFiber.children) {
+        host.removeChild?.(rootFiber.instance as never, child.instance as never, ctx as never);
+      }
+
       host.finalizeRoot?.(ctx);
       host.emit?.("root.unmount", `root_${Date.now()}`, {});
+      this.rootFiber = null;
     },
   };
 }