feat: 站点单页、时间线导入与行级 BBCode 短代码

首页右栏接入单页入口与公告置顶/全部页；Markdown 编辑器支持可视化时间线与 Git 导入；隐藏块改为 [hide]/[timeline] 命名闭合，并修复单页/公告 GORM 更新只改 updated_at 的问题。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/components/markdown/MdTimeline.tsx

@@ -0,0 +1,67 @@
+import type { ReactNode } from "react";
+import { ExternalLink } from "lucide-react";
+import {
+  groupTimelineByDate,
+  type TimelineItem,
+} from "@/lib/timelineBlocks";
+
+type MdTimelineProps = {
+  items: TimelineItem[];
+  /** 每项正文已渲染的 React 节点（与 items 等长）；缺省则只显示纯文本 */
+  renderBody?: (item: TimelineItem, index: number) => ReactNode;
+};
+
+/**
+ * 按日分组的垂直时间线（更新树）。颜色走 CSS 令牌。
+ */
+export default function MdTimeline({ items, renderBody }: MdTimelineProps) {
+  if (!items.length) {
+    return <p className="meta px-1 py-2">暂无时间线条目</p>;
+  }
+  const groups = groupTimelineByDate(items);
+  let flat = 0;
+
+  return (
+    <div className="j13-timeline" role="list" aria-label="时间线">
+      {groups.map((g) => (
+        <div key={g.date} className="j13-timeline-day">
+          <div className="j13-timeline-day-label">
+            <time dateTime={g.date}>{g.date}</time>
+          </div>
+          <ul className="j13-timeline-items">
+            {g.items.map((it) => {
+              const idx = flat++;
+              return (
+                <li key={`${g.date}-${idx}-${it.title}`} className="j13-timeline-item" role="listitem">
+                  <span className="j13-timeline-dot" aria-hidden />
+                  <div className="j13-timeline-card">
+                    <div className="j13-timeline-head">
+                      <h3 className="j13-timeline-title">{it.title}</h3>
+                      {it.sourceUrl ? (
+                        <a
+                          href={it.sourceUrl}
+                          className="j13-timeline-src"
+                          target="_blank"
+                          rel="noopener noreferrer"
+                          data-tip="查看提交"
+                          aria-label="查看提交"
+                        >
+                          <ExternalLink size={13} />
+                        </a>
+                      ) : null}
+                    </div>
+                    {renderBody ? (
+                      <div className="j13-timeline-body">{renderBody(it, idx)}</div>
+                    ) : it.body.trim() ? (
+                      <div className="j13-timeline-body whitespace-pre-wrap">{it.body}</div>
+                    ) : null}
+                  </div>
+                </li>
+              );
+            })}
+          </ul>
+        </div>
+      ))}
+    </div>
+  );
+}