feat: 新增大量社区功能与基础组件，优化站点整体体验

- 新增事件总线式toast通知系统
- 新增头像、阅读进度、404/500错误页等基础组件
- 重构页脚、布局、分页、点赞按钮等现有组件
- 新增用户个人页、通知中心、帖子编辑/发布/置顶/推荐管理功能
- 优化登录注册页面样式与交互
- 修复路径类型文件引用，更新站点元信息与字体配置

frontend/components/Toaster.tsx

@@ -0,0 +1,66 @@
+"use client";
+
+import { useEffect, useState } from "react";
+import { X, AlertCircle, CheckCircle2 } from "lucide-react";
+import type { ToastDetail } from "@/lib/toast";
+
+export default function Toaster() {
+  const [items, setItems] = useState<ToastDetail[]>([]);
+
+  useEffect(() => {
+    const handler = (e: Event) => {
+      const detail = (e as CustomEvent<ToastDetail>).detail;
+      setItems((list) => [...list.slice(-2), detail]);
+      window.setTimeout(() => {
+        setItems((list) => list.filter((t) => t.id !== detail.id));
+      }, 3600);
+    };
+    window.addEventListener("j13-toast", handler);
+    return () => window.removeEventListener("j13-toast", handler);
+  }, []);
+
+  const dismiss = (id: number) => setItems((list) => list.filter((t) => t.id !== id));
+
+  return (
+    <div
+      className="fixed bottom-5 right-4 sm:right-6 z-[10000] flex flex-col gap-2 w-[calc(100vw-2rem)] sm:w-80"
+      aria-live="polite"
+      role="status"
+    >
+      {items.map((t) => (
+        <ToastCard key={t.id} toast={t} onClose={() => dismiss(t.id)} />
+      ))}
+    </div>
+  );
+}
+
+function ToastCard({ toast, onClose }: { toast: ToastDetail; onClose: () => void }) {
+  const color = toast.variant === "error" ? "var(--danger)" : "var(--ok)";
+  return (
+    <div
+      className="j13-toast-in flex items-start gap-3 px-4 py-3.5"
+      style={{
+        background: "var(--panel)",
+        border: "1px solid var(--line)",
+        borderLeft: `3px solid ${color}`,
+        borderRadius: "var(--r-sm)",
+        boxShadow: "var(--shadow-lg)",
+      }}
+      role="alert"
+    >
+      <span className="shrink-0 mt-0.5" style={{ color }}>
+        {toast.variant === "error" ? <AlertCircle size={16} /> : <CheckCircle2 size={16} />}
+      </span>
+      <p className="flex-1 text-[13.5px] leading-snug" style={{ color: "var(--ink)" }}>
+        {toast.message}
+      </p>
+      <button
+        onClick={onClose}
+        className="shrink-0 meta hover:text-[var(--ink)] transition-colors"
+        aria-label="关闭提示"
+      >
+        <X size={14} />
+      </button>
+    </div>
+  );
+}