feat: UOOC/Zhihuishu dual-platform brushing platform

- ASP.NET Core 9 Web API backend with JWT auth, EF Core MySQL
- Vue 3 + Vite + Pinia + Ant Design Vue frontend
- Multi-platform connection management (UOOC & Zhihuishu)
- Video brushing with AES-CBC encryption for Zhihuishu
- Multi-task queue with cross-platform parallel execution
- Task persistence via MySQL database
- Progress tracking with inline catalog enrichment
- Mobile-responsive UI

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

frontend/src/lib/storage.ts

@@ -0,0 +1,60 @@
+const isBrowser = typeof window !== 'undefined';
+
+const rootKey = 'uooc-progress';
+
+export const storageKeys = {
+  accessToken: `${rootKey}:access-token`,
+  selectedPlatformId: (userId: number) => `${rootKey}:user:${userId}:selected-platform-id`,
+  selectedCourseIds: (userId: number) => `${rootKey}:user:${userId}:selected-course-map`,
+  courseOptions: (userId: number) => `${rootKey}:user:${userId}:course-options`,
+  progressSnapshots: (userId: number) => `${rootKey}:user:${userId}:progress-snapshots`,
+};
+
+export function readText(key: string, fallback = ''): string {
+  if (!isBrowser) {
+    return fallback;
+  }
+
+  return window.localStorage.getItem(key) ?? fallback;
+}
+
+export function writeText(key: string, value: string): void {
+  if (!isBrowser) {
+    return;
+  }
+
+  window.localStorage.setItem(key, value);
+}
+
+export function removeKey(key: string): void {
+  if (!isBrowser) {
+    return;
+  }
+
+  window.localStorage.removeItem(key);
+}
+
+export function readJson<T>(key: string, fallback: T): T {
+  if (!isBrowser) {
+    return fallback;
+  }
+
+  const raw = window.localStorage.getItem(key);
+  if (!raw) {
+    return fallback;
+  }
+
+  try {
+    return JSON.parse(raw) as T;
+  } catch {
+    return fallback;
+  }
+}
+
+export function writeJson<T>(key: string, value: T): void {
+  if (!isBrowser) {
+    return;
+  }
+
+  window.localStorage.setItem(key, JSON.stringify(value));
+}