feat: 实现联系表单提交与邮件通知功能

添加联系表单提交接口和邮件通知功能，支持从环境变量读取 SMTP 配置
重构 SEO 配置到 site.json，新增 robots.txt 和 sitemap.xml 生成
更新公司电话并添加 PM2 生产运行配置

lib/seo.ts

@@ -0,0 +1,145 @@
+import type { Metadata, MetadataRoute } from "next"
+import siteData from "@/data/site.json"
+
+type SiteSeoConfig = {
+  siteUrl: string
+  siteName: string
+  defaultTitle: string
+  titleTemplate: string
+  description: string
+  keywords: string[]
+  canonicalPath: string
+  locale?: string
+  robots?: {
+    index?: boolean
+    follow?: boolean
+  }
+  openGraph?: {
+    type?: "website" | "article"
+    image?: string
+  }
+  twitter?: {
+    card?: "summary" | "summary_large_image" | "app" | "player"
+    site?: string
+    creator?: string
+  }
+  verification?: {
+    google?: string
+    yandex?: string
+    other?: Record<string, string>
+  }
+}
+
+const seo = siteData.seo as SiteSeoConfig
+
+function nonEmpty(value?: string) {
+  if (!value) {
+    return undefined
+  }
+
+  const trimmed = value.trim()
+
+  return trimmed ? trimmed : undefined
+}
+
+function getMetadataBase() {
+  return new URL(seo.siteUrl)
+}
+
+function getCanonicalPath() {
+  return nonEmpty(seo.canonicalPath) ?? "/"
+}
+
+function getVerificationOther() {
+  const otherEntries = Object.entries(seo.verification?.other ?? {}).filter(([, value]) => Boolean(nonEmpty(value)))
+
+  return otherEntries.length > 0 ? Object.fromEntries(otherEntries) : undefined
+}
+
+function getOpenGraphImages() {
+  const image = nonEmpty(seo.openGraph?.image)
+
+  return image ? [{ url: image }] : undefined
+}
+
+export function buildSiteMetadata(): Metadata {
+  const index = seo.robots?.index ?? true
+  const follow = seo.robots?.follow ?? true
+  const verificationOther = getVerificationOther()
+  const canonicalPath = getCanonicalPath()
+  const openGraphImages = getOpenGraphImages()
+
+  return {
+    metadataBase: getMetadataBase(),
+    applicationName: seo.siteName,
+    title: {
+      default: seo.defaultTitle,
+      template: seo.titleTemplate,
+    },
+    description: seo.description,
+    keywords: seo.keywords,
+    authors: [{ name: siteData.company.name }],
+    creator: siteData.company.name,
+    publisher: siteData.company.name,
+    alternates: {
+      canonical: canonicalPath,
+    },
+    robots: {
+      index,
+      follow,
+      googleBot: {
+        index,
+        follow,
+      },
+    },
+    verification: {
+      google: nonEmpty(seo.verification?.google),
+      yandex: nonEmpty(seo.verification?.yandex),
+      other: verificationOther,
+    },
+    openGraph: {
+      title: seo.defaultTitle,
+      description: seo.description,
+      url: canonicalPath,
+      siteName: seo.siteName,
+      locale: nonEmpty(seo.locale),
+      type: seo.openGraph?.type ?? "website",
+      images: openGraphImages,
+    },
+    twitter: {
+      card: seo.twitter?.card ?? "summary_large_image",
+      title: seo.defaultTitle,
+      description: seo.description,
+      images: openGraphImages?.map((image) => image.url),
+      site: nonEmpty(seo.twitter?.site),
+      creator: nonEmpty(seo.twitter?.creator),
+    },
+  }
+}
+
+export function buildRobots(): MetadataRoute.Robots {
+  return {
+    rules: [
+      {
+        userAgent: "*",
+        allow: "/",
+      },
+    ],
+    sitemap: `${seo.siteUrl.replace(/\/$/, "")}/sitemap.xml`,
+    host: seo.siteUrl,
+  }
+}
+
+export function buildSitemap(): MetadataRoute.Sitemap {
+  const canonicalPath = getCanonicalPath()
+  const normalizedSiteUrl = seo.siteUrl.replace(/\/$/, "")
+
+  return [
+    {
+      url: `${normalizedSiteUrl}${canonicalPath}`,
+      lastModified: new Date(),
+      changeFrequency: "weekly",
+      priority: 1,
+    },
+  ]
+}