feat(news): 支持新闻中心多站点隔离功能

新增站点编码配置，支持新闻分类与文章按站点隔离。主要变更包括：
- 数据库表增加 site_code 字段及索引
- 后台管理界面支持按站点筛选
- 前台接口支持通过查询参数或请求头指定站点
- 新增站点配置与解析逻辑

server/target/classes/mapper/NewsCategoryMapper.xml

@@ -7,11 +7,15 @@
     </resultMap>
 
     <select id="selectAll" resultMap="newsCategoryResult">
-        SELECT * FROM f_news_category WHERE del_flag = 0 ORDER BY sort_order ASC
+        SELECT * FROM f_news_category WHERE del_flag = 0
+        <if test="siteCode != null and siteCode != ''">AND site_code = #{siteCode}</if>
+        ORDER BY sort_order ASC
     </select>
 
     <select id="selectPublished" resultMap="newsCategoryResult">
-        SELECT * FROM f_news_category WHERE del_flag = 0 AND is_published = 1 ORDER BY sort_order ASC
+        SELECT * FROM f_news_category WHERE del_flag = 0 AND is_published = 1
+        <if test="siteCode != null and siteCode != ''">AND site_code = #{siteCode}</if>
+        ORDER BY sort_order ASC
     </select>
 
     <select id="selectById" resultMap="newsCategoryResult">
@@ -19,13 +23,14 @@
     </select>
 
     <insert id="insert" useGeneratedKeys="true" keyProperty="newsCategoryId" keyColumn="category_id">
-        INSERT INTO f_news_category (name_zh, name_en, sort_order, is_published, create_by, remark)
-        VALUES (#{nameZh}, #{nameEn}, #{sortOrder}, #{isPublished}, #{createBy}, #{remark})
+        INSERT INTO f_news_category (site_code, name_zh, name_en, sort_order, is_published, create_by, remark)
+        VALUES (#{siteCode}, #{nameZh}, #{nameEn}, #{sortOrder}, #{isPublished}, #{createBy}, #{remark})
     </insert>
 
     <update id="update" parameterType="com.wuhansaga.server.entity.NewsCategory">
         UPDATE f_news_category
         <set>
+            <if test="siteCode != null">site_code = #{siteCode},</if>
             <if test="nameZh != null">name_zh = #{nameZh},</if>
             <if test="nameEn != null">name_en = #{nameEn},</if>
             <if test="sortOrder != null">sort_order = #{sortOrder},</if>