feat: 添加 PWA 支持和 SEO 优化

添加 PWA manifest 文件、favicon、结构化数据、sitemap 和 robots.txt。
优化根布局和组件的国际化支持，包括服务端语言检测和防止水合闪烁。

src/app/(dashboard)/tools/texture-atlas/layout.tsx

@@ -0,0 +1,67 @@
+import type { Metadata } from "next";
+import { headers } from "next/headers";
+
+export async function generateMetadata(): Promise<Metadata> {
+  const headersList = await headers();
+  const acceptLanguage = headersList.get("accept-language") || "";
+  const lang = acceptLanguage.includes("zh") ? "zh" : "en";
+
+  const titles = {
+    en: "Texture Atlas Generator - Create Sprite Sheets Online",
+    zh: "纹理图集生成器 - 在线创建精灵图",
+  };
+
+  const descriptions = {
+    en: "Generate texture atlases and sprite sheets for game development. Pack multiple sprites into a single texture atlas with JSON data export. All processing happens locally in your browser.",
+    zh: "为游戏开发生成纹理图集和精灵图。将多个精灵打包到单个纹理图集中，支持导出 JSON 数据。所有处理都在您的浏览器本地进行。",
+  };
+
+  const keywords = {
+    en: [
+      "texture atlas",
+      "sprite sheet",
+      "game development",
+      "sprite packer",
+      "texture packing",
+      "game assets",
+      "sprite generator",
+      "JSON export",
+      "browser-based",
+    ],
+    zh: [
+      "纹理图集",
+      "精灵图",
+      "游戏开发",
+      "精灵打包",
+      "纹理打包",
+      "游戏资产",
+      "精灵生成器",
+      "JSON导出",
+      "浏览器端",
+    ],
+  };
+
+  return {
+    title: titles[lang],
+    description: descriptions[lang],
+    keywords: keywords[lang],
+    openGraph: {
+      title: titles[lang],
+      description: descriptions[lang],
+      type: "website",
+    },
+    twitter: {
+      title: titles[lang],
+      description: descriptions[lang],
+      card: "summary_large_image",
+    },
+  };
+}
+
+export default function TextureAtlasLayout({
+  children,
+}: {
+  children: React.ReactNode;
+}) {
+  return children;
+}