refactor: 项目管理菜单改造为下拉导航组

- 新增 SidebarNavGroup 组件支持可展开导航组
- 路由从 /console/projects 调整为 /console/project/*
- 成员管理页面独立为子菜单
- 新增权限配置、技能配置占位页面
- URL 驱动展开状态，刷新保持
- 更新 README.md 和 specs

src/styles/components/nav/_index.scss

@@ -46,3 +46,62 @@
     font-size: $font-size-sm;
     color: var(--color-text-3);
 }
+
+// 可展开导航组
+.nav-group {
+    margin-bottom: 4px;
+}
+
+.nav-group__header {
+    display: flex;
+    align-items: center;
+    gap: 10px;
+    padding: 10px 12px;
+    border-radius: var(--radius-md);
+    cursor: pointer;
+    transition: background 0.2s;
+    color: var(--color-text-2);
+    font-size: $font-size-base;
+    font-weight: $font-weight-medium;
+
+    &:hover {
+        background: var(--color-bg-2);
+        color: var(--color-text-1);
+    }
+}
+
+.nav-group__icon {
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    width: 20px;
+    height: 20px;
+    font-size: $font-size-lg;
+    flex-shrink: 0;
+}
+
+.nav-group__label {
+    flex: 1;
+}
+
+.nav-group__arrow {
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    width: 16px;
+    height: 16px;
+    font-size: $font-size-sm;
+    color: var(--color-text-3);
+    transition: transform 0.2s;
+}
+
+.nav-group__children {
+    margin-top: 4px;
+    padding-left: 12px;
+}
+
+.nav-group--expanded {
+    .nav-group__header {
+        color: var(--color-text-1);
+    }
+}