frontend: rebuild bookmark page with drag-and-drop, search, and theme system

- bookmark management with dnd-kit reordering, bulk edit, search,
  category filter/rename, and meta auto-fetch
- migrate /bookmarks → /dashboard/bookmarks under (main) layout
- homepage redesign with category grid, /-key search, dock tooltips
- theme toggle + use-theme, sonner toasts, alert-dialog/skeleton,
  visual refresh of auth pages

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/lib/bookmarks.ts

@@ -0,0 +1,143 @@
+export interface BookmarkLite {
+  title: string;
+  url: string;
+  description?: string;
+  icon?: string;
+  category?: string;
+  sortOrder?: number;
+}
+
+export function hostnameOf(raw: string): string {
+  try {
+    const u = new URL(raw.includes("://") ? raw : `https://${raw}`);
+    return u.hostname.replace(/^www\./, "");
+  } catch {
+    return "";
+  }
+}
+
+export function faviconFallback(url: string, size = 64): string {
+  const host = hostnameOf(url);
+  if (!host) return "";
+  return `https://www.google.com/s2/favicons?domain=${host}&sz=${size}`;
+}
+
+export function normalizeURL(raw: string): string {
+  const trimmed = raw.trim();
+  if (!trimmed) return "";
+  if (/^https?:\/\//i.test(trimmed)) return trimmed;
+  return `https://${trimmed}`;
+}
+
+export function exportToJSON(bookmarks: BookmarkLite[]): string {
+  return JSON.stringify(
+    {
+      exportedAt: new Date().toISOString(),
+      bookmarks: bookmarks.map((b) => ({
+        title: b.title,
+        url: b.url,
+        description: b.description ?? "",
+        icon: b.icon ?? "",
+        category: b.category ?? "默认",
+        sortOrder: b.sortOrder ?? 0,
+      })),
+    },
+    null,
+    2,
+  );
+}
+
+export function downloadFile(filename: string, content: string, mime = "application/json") {
+  const blob = new Blob([content], { type: `${mime};charset=utf-8` });
+  const url = URL.createObjectURL(blob);
+  const a = document.createElement("a");
+  a.href = url;
+  a.download = filename;
+  a.click();
+  setTimeout(() => URL.revokeObjectURL(url), 1000);
+}
+
+export function parseImport(text: string): BookmarkLite[] {
+  const trimmed = text.trim();
+  if (!trimmed) return [];
+
+  if (trimmed.startsWith("{") || trimmed.startsWith("[")) {
+    return parseJSON(trimmed);
+  }
+  if (trimmed.toLowerCase().includes("<!doctype netscape-bookmark") || trimmed.toLowerCase().includes("<dl")) {
+    return parseNetscapeHTML(trimmed);
+  }
+
+  return parseJSON(trimmed);
+}
+
+function parseJSON(raw: string): BookmarkLite[] {
+  try {
+    const parsed = JSON.parse(raw);
+    const list: unknown[] = Array.isArray(parsed)
+      ? parsed
+      : Array.isArray((parsed as { bookmarks?: unknown[] })?.bookmarks)
+        ? (parsed as { bookmarks: unknown[] }).bookmarks
+        : [];
+    return list
+      .map((item) => {
+        const i = item as Record<string, unknown>;
+        return {
+          title: String(i.title ?? i.name ?? "").trim(),
+          url: String(i.url ?? i.href ?? "").trim(),
+          description: i.description ? String(i.description) : "",
+          icon: i.icon ? String(i.icon) : "",
+          category: i.category ? String(i.category) : "默认",
+          sortOrder: typeof i.sortOrder === "number" ? i.sortOrder : 0,
+        };
+      })
+      .filter((b) => b.title && b.url);
+  } catch {
+    return [];
+  }
+}
+
+function parseNetscapeHTML(raw: string): BookmarkLite[] {
+  if (typeof DOMParser === "undefined") return [];
+  const doc = new DOMParser().parseFromString(raw, "text/html");
+  const out: BookmarkLite[] = [];
+
+  const walk = (node: Element, currentCategory: string) => {
+    const children = Array.from(node.children);
+    for (let i = 0; i < children.length; i++) {
+      const el = children[i];
+      const tag = el.tagName.toLowerCase();
+      if (tag === "dt") {
+        const inner = el.firstElementChild;
+        if (!inner) continue;
+        const innerTag = inner.tagName.toLowerCase();
+        if (innerTag === "a") {
+          const a = inner as HTMLAnchorElement;
+          const href = a.getAttribute("href") || "";
+          const title = (a.textContent || "").trim() || href;
+          const icon = a.getAttribute("icon") || "";
+          if (href && /^https?:\/\//i.test(href)) {
+            out.push({
+              title,
+              url: href,
+              description: "",
+              icon,
+              category: currentCategory || "默认",
+              sortOrder: 0,
+            });
+          }
+        } else if (innerTag === "h3") {
+          const folderName = (inner.textContent || "").trim() || currentCategory;
+          const dl = el.querySelector("dl");
+          if (dl) walk(dl, folderName);
+        }
+      } else if (tag === "dl") {
+        walk(el, currentCategory);
+      }
+    }
+  };
+
+  const root = doc.querySelector("dl");
+  if (root) walk(root, "默认");
+  return out;
+}