公开页补齐自引用 Canonical 与按类型的结构化数据，图片补上说明文字。

后台设置和内容编辑改成可导航布局；部署用访客 origin 生成 Canonical，避免落到容器地址。

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

frontend/lib/siteUrl.ts

@@ -0,0 +1,151 @@
+import type { Metadata } from "next";
+
+/**
+ * 公开站点 origin（访客浏览器地址栏），与 Go CORS 的 SITE_URL 同源。
+ * 不使用 BACKEND_URL / NEXT_PUBLIC_API_URL（那是 Go API，可能是容器内网）。
+ */
+
+const TRACKING_KEYS = new Set([
+  "gclid",
+  "gbraid",
+  "wbraid",
+  "dclid",
+  "fbclid",
+  "msclkid",
+  "twclid",
+  "ttclid",
+  "yclid",
+  "_ga",
+  "_gl",
+  "mc_cid",
+  "mc_eid",
+]);
+
+export type QueryValue = string | number | undefined | null;
+export type QueryBag = Record<string, QueryValue>;
+export type FeedSort = "latest" | "new" | "recommended";
+
+function envOriginRaw(): string {
+  return (process.env.SITE_URL || "").trim();
+}
+
+/** 解析为无尾斜杠的 http(s) origin；路径/账号/内部服务名视为非法 */
+export function parseSiteOrigin(raw: string | undefined | null): string | null {
+  const s = raw?.trim() ?? "";
+  if (!s) return null;
+  let u: URL;
+  try {
+    u = new URL(s);
+  } catch {
+    return null;
+  }
+  if (u.protocol !== "http:" && u.protocol !== "https:") return null;
+  if (u.username || u.password) return null;
+  const host = u.hostname.toLowerCase();
+  if (!host || host === "api" || host.endsWith(".internal")) return null;
+  const path = u.pathname.replace(/\/+$/, "");
+  if (path !== "") return null;
+  return `${u.protocol}//${u.host}`;
+}
+
+/**
+ * 运行时公开 origin。
+ * 开发态未配置时用 http://localhost:3000；生产态缺失或非法则返回 null（不回退 localhost）。
+ */
+export function resolveSiteOrigin(): string | null {
+  const parsed = parseSiteOrigin(envOriginRaw());
+  if (parsed) return parsed;
+  if (process.env.NODE_ENV !== "production") return "http://localhost:3000";
+  return null;
+}
+
+export function metadataBaseURL(): URL | undefined {
+  const origin = resolveSiteOrigin();
+  return origin ? new URL(`${origin}/`) : undefined;
+}
+
+export function isTrackingParam(key: string): boolean {
+  const k = key.toLowerCase();
+  return k.startsWith("utm_") || TRACKING_KEYS.has(k);
+}
+
+/** 路径规范化：保证以 / 开头，除首页外去掉尾斜杠 */
+export function canonicalPath(pathname: string, query?: QueryBag): string {
+  let path = pathname.trim() || "/";
+  if (!path.startsWith("/")) path = `/${path}`;
+  if (path.length > 1) path = path.replace(/\/+$/, "");
+  const params = new URLSearchParams();
+  if (query) {
+    const keys = Object.keys(query).sort();
+    for (const key of keys) {
+      if (isTrackingParam(key)) continue;
+      const raw = query[key];
+      if (raw == null || raw === "") continue;
+      params.set(key, String(raw));
+    }
+  }
+  const qs = params.toString();
+  return qs ? `${path}?${qs}` : path;
+}
+
+export function absoluteCanonical(pathname: string, query?: QueryBag): string | undefined {
+  const origin = resolveSiteOrigin();
+  if (!origin) return undefined;
+  return `${origin}${canonicalPath(pathname, query)}`;
+}
+
+/** 写入 generateMetadata 的 alternates.canonical；origin 不可用时不加字段 */
+export function canonicalFields(pathname: string, query?: QueryBag): Pick<Metadata, "alternates"> {
+  const href = absoluteCanonical(pathname, query);
+  if (!href) return {};
+  return { alternates: { canonical: href } };
+}
+
+/** 页码：非法或 ≤1 视为首页（省略 page） */
+export function canonicalPage(raw: string | undefined): number | undefined {
+  const n = parseInt(raw || "1", 10);
+  const page = Number.isFinite(n) ? Math.max(1, n) : 1;
+  return page > 1 ? page : undefined;
+}
+
+/** 板块 id：≤0 或非法则省略 */
+export function canonicalBoard(raw: string | undefined): number | undefined {
+  const n = parseInt(raw || "0", 10);
+  if (!Number.isFinite(n) || n <= 0) return undefined;
+  return n;
+}
+
+export function defaultFeedSort(allowComments: boolean): FeedSort {
+  return allowComments ? "latest" : "new";
+}
+
+/** 与首页 page.tsx 的排序解析一致 */
+export function normalizeFeedSort(v: string | undefined, allowComments: boolean): FeedSort {
+  if (v === "recommended") return "recommended";
+  if (v === "new") return "new";
+  if (!allowComments) return "new";
+  if (v === "latest") return "latest";
+  return "latest";
+}
+
+/**
+ * 首页 query 归一化：保留 q / 非默认 sort / 有效 board / page>1；
+ * 搜索时 board 不参与列表查询，故省略。
+ */
+export function homeCanonicalQuery(
+  sp: { q?: string; page?: string; sort?: string; board?: string },
+  allowComments: boolean
+): QueryBag {
+  const q = sp.q?.trim() || "";
+  const bag: QueryBag = {};
+  if (q) bag.q = q;
+  const page = canonicalPage(sp.page);
+  if (page) bag.page = page;
+  const sort = normalizeFeedSort(sp.sort, allowComments);
+  if (sort !== defaultFeedSort(allowComments)) bag.sort = sort;
+  if (!q) {
+    const board = canonicalBoard(sp.board);
+    if (board) bag.board = board;
+  }
+  return bag;
+}