feat(B4): 友链页脚 Logo 渲染-5主题 img+名称并排,渲染期补基准

- PortalLink 模型已有 logoUrl,渲染缺口在模板:5 套 footer 增 th:if logo 图(url.upload 补基准+alt 名称+lazy)
- 5 套 main.css 增 .link-logo(高20px/contain/垂直居中/过宽截断)
- PortalSsrIT+2 例(有 logo 渲染图/无 logo 纯文字无 link-logo);mvn -o test 260/260 全绿

src/main/resources/templates/themes/blue-white/assets/css/main.css

@@ -330,3 +330,15 @@ time, .item-meta { color: var(--text-light); font-size: 13px; }
 .home-main, .list-main, .detail-main { padding-top: 36px; padding-bottom: 56px; }
 .article-list .article-title, .block-head, .page-title { letter-spacing: .02em; }
 .article-list li, .banner, .banner-title { border-radius: 4px; }
+
+/* B4 友链 Logo：与名称并排小图（高度 ~20px，垂直居中；过宽截断不撑破页脚） */
+.links-group a .link-logo,
+.sp-links-row a .link-logo {
+    height: 20px;
+    width: auto;
+    max-width: 64px;
+    object-fit: contain;
+    vertical-align: middle;
+    margin-right: 4px;
+    border-radius: 2px;
+}