feat(web): 插件侧边栏改为三级菜单结构 — 按插件名分组可折叠

插件菜单从扁平列表改为三级结构：
  插件（分组）→ 插件名（可折叠子标题）→ 页面列表

- store 新增 PluginMenuGroup 类型和 pluginMenuGroups getter
- MainLayout 新增 SidebarSubMenu 组件，支持展开/收起
- 折叠侧边栏时子菜单显示插件图标 + tooltip
- 子菜单项增加缩进样式区分层级
- CRM 插件 name 改为 "CRM" 避免与页面标题重名

apps/web/src/index.css

@@ -658,6 +658,50 @@ body {
   margin-left: 12px;
 }
 
+/* Sidebar sub-menu (plugin group) */
+.erp-sidebar-submenu-title {
+  display: flex;
+  align-items: center;
+  height: 32px;
+  margin: 6px 8px 2px 8px;
+  padding: 0 12px;
+  border-radius: 6px;
+  cursor: pointer;
+  color: #94A3B8;
+  font-size: 12px;
+  font-weight: 600;
+  text-transform: uppercase;
+  letter-spacing: 0.5px;
+  transition: all 0.15s;
+  user-select: none;
+}
+
+.erp-sidebar-submenu-title:hover {
+  background: rgba(255, 255, 255, 0.06);
+  color: #E2E8F0;
+}
+
+.erp-sidebar-submenu-title-active {
+  color: #A5B4FC;
+}
+
+.erp-sidebar-submenu-arrow {
+  display: flex;
+  align-items: center;
+  margin-right: 8px;
+  font-size: 10px;
+}
+
+.erp-sidebar-submenu-label {
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis;
+}
+
+.erp-sidebar-item-indented {
+  padding-left: 36px;
+}
+
 /* Main layout */
 .erp-main-layout {
   transition: margin-left 0.2s cubic-bezier(0.4, 0, 0.2, 1);