feat(content): 分组对所有内容类型生效，统一分区/分组/条目模型

- 分区=容器，分组=任意类型的可选子容器，条目可挂分区或分组（直属分区）
- catalog 所有类型统一输出 groups + items，条目查询按节点取
- 详情/侧栏/首页卡片预览支持所有类型的分组；多组显示小标题 + 未分组
- 后台「分区」「侧栏导航」对所有类型可建组；「内容」弹窗分组可选直属分区，编辑可换组
- 修复首页卡片配置为「整个分区」时预览为空
- 测试 59 passed

src/db/categories.rs

@@ -361,22 +361,17 @@ pub fn create_group(conn: &mut Connection, section_id: &str, new: NewGroup) -> R
         return Err(StashError::InvalidDirectory("分组标题需为 1–40 个字".into()));
     }
 
-    let view_mode: Option<String> = conn
+    let section_exists: Option<String> = conn
         .query_row(
-            "SELECT view_mode FROM node WHERE key = ?1 AND kind = 'section'",
+            "SELECT key FROM node WHERE key = ?1 AND kind = 'section'",
             [section_id],
             |row| row.get(0),
         )
         .optional()
         .map_err(map_error)?;
 
-    let Some(view_mode) = view_mode else {
+    if section_exists.is_none() {
         return Err(StashError::NotFound(format!("分区不存在: {section_id}")));
-    };
-    if view_mode != "apps" {
-        return Err(StashError::InvalidDirectory(
-            "只有应用类分区可以添加分组".into(),
-        ));
     }
 
     let exists: i64 = conn
@@ -712,21 +707,18 @@ mod tests {
     }
 
     #[test]
-    fn groups_only_under_apps_sections() {
+    fn groups_under_any_kind_of_section() {
         let mut conn = db();
         create(&mut conn, section("films", "电影", "posters")).expect("应能创建");
-        assert!(
-            create_group(
-                &mut conn,
-                "films",
-                NewGroup {
-                    id: "g1".into(),
-                    title: "分组".into()
-                }
-            )
-            .is_err(),
-            "海报分区不能建分组"
-        );
+        create_group(
+            &mut conn,
+            "films",
+            NewGroup {
+                id: "g1".into(),
+                title: "片单".into(),
+            },
+        )
+        .expect("海报分区也应能建分组");
     }
 
     #[test]