fix: 创建产品后要刷新才出现 + 刷新后已有产品的项目被清空

根因：
1. createProduct try 路径调 fetchOverview，但 fetchOverview 第 103 行
   `if (overview.length > 0) return` 直接 early return，导致新产品没被加进
   overview，需刷新才能从 localStorage 重读。
2. fetchOverview 在 cached 已有数据时仍会调 api.get 拉远端，远端 mock
   返回简化数据（无 projects）覆盖整个 overview，导致已有产品下的项目消失。

修复（mock 模式核心数据完全本地化）：
- createProduct：直接本地新增 + saveLocal，异步尝试远端但不依赖（不再调
  fetchOverview）
- fetchOverview：cached 有数据时直接用，不再调远端覆盖；空时才走远端/MOCK 路径

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/stores/useProductStore.ts

@@ -102,18 +102,19 @@ export const useProductStore = create<ProductState>((set, get) => ({
   fetchOverview: async () => {
     if (get().overview.length > 0) return;
     const cached = loadLocal();
-    if (cached.length > 0) set({ overview: cached, loading: false });
-    else set({ loading: true, error: null });
+    if (cached.length > 0) {
+      // 有本地缓存，直接用，不再调远端覆盖（mock 模式核心数据在本地）
+      set({ overview: cached, loading: false });
+      return;
+    }
+    set({ loading: true, error: null });
     try {
       const overview = await api.get<ProductOverview[]>('/products/overview');
       set({ overview, loading: false });
       saveLocal(overview);
     } catch {
-      if (cached.length === 0) {
-        set({ overview: MOCK_OVERVIEW, error: null, loading: false });
-      } else {
-        set({ loading: false });
-      }
+      set({ overview: MOCK_OVERVIEW, error: null, loading: false });
+      saveLocal(MOCK_OVERVIEW);
     }
   },
 
@@ -133,24 +134,22 @@ export const useProductStore = create<ProductState>((set, get) => ({
   },
 
   createProduct: async (data) => {
-    try {
-      await api.post('/products', data);
-      await get().fetchOverview();
-    } catch {
-      const newProduct: ProductOverview = {
-        id: `local-${Date.now()}`,
-        name: data.name || '',
-        description: data.description || '',
-        createdAt: new Date().toISOString(),
-        updatedAt: new Date().toISOString(),
-        projects: [],
-        versions: [],
-        _count: { requirements: 0, projects: 0, versions: 0 },
-      };
-      const updated = [newProduct, ...get().overview];
-      set({ overview: updated });
-      saveLocal(updated);
-    }
+    // 直接本地新增（mock 模式核心，保留远端兼容但不依赖）
+    const newProduct: ProductOverview = {
+      id: `local-${Date.now()}`,
+      name: data.name || '',
+      description: data.description || '',
+      createdAt: new Date().toISOString(),
+      updatedAt: new Date().toISOString(),
+      projects: [],
+      versions: [],
+      _count: { requirements: 0, projects: 0, versions: 0 },
+    };
+    const updated = [newProduct, ...get().overview];
+    set({ overview: updated });
+    saveLocal(updated);
+    // 异步尝试同步远端（失败也无所谓，本地已更新）
+    try { await api.post('/products', data); } catch {}
   },
 
   updateProduct: async (id, data) => {