feat: 友链/书库/移动端导航/排行榜等多模块功能

新增模块：
- 友链（friendlink）后端处理 + 前端管理页与友链板
- 书库（library）：导入、章节、封面、阅读页、横竖版自适应 AdaptiveCoverSlot
- 顶栏导航（header_nav）配置与 MobileTabBar/MobileRailDrawers 移动端抽屉
- 排行榜 service 测试、站点页面测试、时间线发布（timeline_release）

其它改动：
- 后端 handlers/services 全量小幅调整
- 前端组件、库函数、URL/品牌/站点 URL 工具更新
- Lightbox 图片、MdEntries 条目卡、coverColor 派生色相等前端能力

frontend/app/admin/settings/BrandSeoPanel.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { ImagePlus, Images, X } from "lucide-react";
+import { Check, ImagePlus, Images, Link2, X } from "lucide-react";
 import { useEffect, useRef, useState, type Dispatch, type SetStateAction } from "react";
 import {
   AdminSegmented,
@@ -13,6 +13,7 @@ import {
   BRAND_LOGO_FITS,
   BRAND_LOGO_SIZES,
   brandAccept,
+  brandAliasPath,
   brandFileOk,
   type BrandLogoFit,
   type BrandLogoSize,
@@ -75,6 +76,7 @@ export default function BrandSeoPanel({
   const [saving, setSaving] = useState(false);
   const [saveError, setSaveError] = useState("");
   const [picker, setPicker] = useState<BrandSlot | null>(null);
+  const [copiedSlot, setCopiedSlot] = useState<BrandSlot | null>(null);
   const blobs = useRef<string[]>([]);
   const saveGen = useRef(0);
 
@@ -203,6 +205,21 @@ export default function BrandSeoPanel({
   const slotDraft = (id: BrandSlot) =>
     id === "logo_dark" ? dark : id === "favicon" ? favicon : light;
 
+  // 已保存的槽位 URL：存在才展示固定地址（未保存过无图可引用）
+  const savedOf = (slot: BrandSlot) =>
+    slot === "logo_dark" ? saved.dark : slot === "favicon" ? saved.favicon : saved.light;
+
+  const copyAlias = async (slot: BrandSlot) => {
+    try {
+      await navigator.clipboard.writeText(`${window.location.origin}${brandAliasPath(slot)}`);
+      setCopiedSlot(slot);
+      toast("已复制固定地址", "ok");
+      window.setTimeout(() => setCopiedSlot((cur) => (cur === slot ? null : cur)), 1500);
+    } catch {
+      toast("复制失败，请手动复制");
+    }
+  };
+
   const renderSlot = (slot: BrandSlot, label: string, swatch: "light" | "dark" | "neutral", compact?: boolean) => {
     const draft = slotDraft(slot);
     const preview = previewOf(draft);
@@ -224,6 +241,18 @@ export default function BrandSeoPanel({
         </div>
         <div className="admin-brand-asset-meta">
           <span className="admin-brand-asset-label">{label}</span>
+          {savedOf(slot) ? (
+            <button
+              type="button"
+              className="admin-brand-alias"
+              title="点击复制固定地址（换图不变链，友链引用请用此地址）"
+              onClick={() => void copyAlias(slot)}
+            >
+              <Link2 size={12} aria-hidden />
+              <span className="admin-brand-alias-url">{brandAliasPath(slot)}</span>
+              {copiedSlot === slot ? <Check size={12} aria-hidden /> : null}
+            </button>
+          ) : null}
           <div className="admin-brand-asset-actions">
             <label className="btn btn-line btn-sm cursor-pointer">
               <ImagePlus size={14} /> 上传