fix(widgets): remove out-of-scope UniFi OS widget stub from task 6

The widget stub (packages/widgets/src/unifi-os/) was incorrectly added in
Task 6 and belongs to Task 7. Its removal confirms the type system does not
require it, and prevents inconsistencies: the stub declares IconWifi while
Task 7 specifies IconRouter, and it is not registered in manifest.ts,
catalog.ts or refetch-intervals.ts.

- Delete packages/widgets/src/unifi-os/ directory entirely
- Revert packages/widgets/src/index.tsx to commit 57286d83d

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

packages/widgets/src/unifi-os/component.tsx

@@ -1,7 +0,0 @@
-"use client";
-
-import type { WidgetComponentProps } from "../definition";
-
-export default function UnifiOsWidgetComponent({ integrationIds }: WidgetComponentProps<"unifiOs">) {
-  return <div>UniFi OS Widget</div>;
-}

packages/widgets/src/unifi-os/index.ts

@@ -1,12 +0,0 @@
-import { IconWifi } from "@tabler/icons-react";
-
-import { createWidgetDefinition } from "../definition";
-import { optionsBuilder } from "../options";
-
-export const { definition, componentLoader } = createWidgetDefinition("unifiOs", {
-  icon: IconWifi,
-  createOptions() {
-    return optionsBuilder.from((factory) => ({}));
-  },
-  supportedIntegrations: ["unifiOs"],
-}).withDynamicImport(() => import("./component"));