feat: 添加移动端下拉菜单和主题色设置

- 新增 MobileMenu 组件，小屏幕使用汉堡菜单替代多个按钮
- 重构 LanguageSettings 为统一下拉框样式
- 新增设置页面，支持主题色切换
- 翻译页添加源语言选择器
- 更新 8 种语言的 i18n 翻译

src/components/layout/MobileMenu.tsx

@@ -0,0 +1,92 @@
+"use client";
+
+import { useState, useEffect, useRef } from "react";
+import { Menu, X } from "lucide-react";
+import { cn } from "@/utils/cn";
+import type { NavigationItem } from "./Navbar";
+
+interface MobileMenuProps {
+  items: NavigationItem[];
+}
+
+export function MobileMenu({ items }: MobileMenuProps) {
+  const [isOpen, setIsOpen] = useState(false);
+  const menuRef = useRef<HTMLDivElement>(null);
+
+  useEffect(() => {
+    const handleClickOutside = (event: MouseEvent) => {
+      if (menuRef.current && !menuRef.current.contains(event.target as Node)) {
+        setIsOpen(false);
+      }
+    };
+
+    if (isOpen) {
+      document.addEventListener("mousedown", handleClickOutside);
+      document.body.style.overflow = "hidden";
+    }
+
+    return () => {
+      document.removeEventListener("mousedown", handleClickOutside);
+      document.body.style.overflow = "";
+    };
+  }, [isOpen]);
+
+  useEffect(() => {
+    const handleEscape = (e: KeyboardEvent) => {
+      if (e.key === "Escape") setIsOpen(false);
+    };
+
+    if (isOpen) {
+      document.addEventListener("keydown", handleEscape);
+      return () => document.removeEventListener("keydown", handleEscape);
+    }
+  }, [isOpen]);
+
+  return (
+    <div className="relative" ref={menuRef}>
+      <button
+        onClick={() => setIsOpen(!isOpen)}
+        className="flex items-center justify-center p-2 rounded-md text-white hover:bg-white/10 transition-colors"
+        aria-label={isOpen ? "关闭菜单" : "打开菜单"}
+        aria-expanded={isOpen}
+      >
+        {isOpen ? <X size={24} /> : <Menu size={24} />}
+      </button>
+
+      <div
+        className={cn(
+          "absolute right-0 top-full mt-2 w-56 rounded-lg bg-white shadow-lg ring-1 ring-black/5 overflow-hidden transition-all duration-200 origin-top-right z-50",
+          isOpen
+            ? "opacity-100 scale-100"
+            : "opacity-0 scale-95 pointer-events-none"
+        )}
+        role="menu"
+      >
+        <div className="py-1">
+          {items.map((item, index) => (
+            <a
+              key={index}
+              href={item.href}
+              className="flex items-center gap-3 px-4 py-3 text-gray-700 hover:bg-gray-50 hover:text-gray-900 transition-colors"
+              role="menuitem"
+              onClick={() => setIsOpen(false)}
+              target={item.external ? "_blank" : undefined}
+              rel={item.external ? "noopener noreferrer" : undefined}
+            >
+              {item.icon && <span className="shrink-0 text-gray-500">{item.icon}</span>}
+              <span>{item.label}</span>
+            </a>
+          ))}
+        </div>
+      </div>
+
+      {isOpen && (
+        <div
+          className="fixed inset-0 z-40"
+          onClick={() => setIsOpen(false)}
+          aria-hidden="true"
+        />
+      )}
+    </div>
+  );
+}