feat(studio): studio web UI (course list, manifest, lessons with live preview, decks, attachments, exercises, conflicts, sync) and dev entry

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/feature-studio/src/web.ts

@@ -0,0 +1,12 @@
+import type { WebFeature } from "@stc/contracts";
+
+/** Studio web routes. The pages call /api/studio, which allows only owners, authors and per-course authors. */
+export const studioWeb: WebFeature = {
+  name: "studio",
+  routes: [
+    { path: "/studio", element: () => import("./ui/StudioHome"), nav: { label: "Studio", area: "header" } },
+    { path: "/studio/:courseId", element: () => import("./ui/CourseStudio") },
+  ],
+};
+
+export { setLessonPreview, type LessonPreviewProps, type LessonPreviewComponent } from "./ui/preview";