chore: optimize SEO and fix golangci-lint issues

- Implement dynamic SEO meta tags and sitemap.xml for toolbox.pengzhan.dev
- Fix SPA title/meta refresh issue in layout.html
- Address golangci-lint findings:
  - Refactor switch-case for tool path and SVG token parsing
  - Replace math.Pow with direct multiplication for performance
  - Fix unhandled error returns and unused imports
  - Omit redundant type declarations

cmd/toolbox/main.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"embed"
 	"flag"
+	"fmt"
 	"html/template"
 	"io/fs"
 	"log"
@@ -56,6 +57,23 @@ func main() {
 	subFS, _ := fs.Sub(webFS, "web")
 	r.StaticFS("/static", http.FS(subFS))
 
+	// 2.5 SEO 静态文件映射
+	r.GET("/robots.txt", func(c *gin.Context) {
+		c.String(http.StatusOK, "User-agent: *\nAllow: /\nSitemap: https://toolbox.pengzhan.dev/sitemap.xml\n")
+	})
+	r.GET("/sitemap.xml", func(c *gin.Context) {
+		var buf bytes.Buffer
+		buf.WriteString("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n")
+		buf.WriteString("<urlset xmlns=\"http://www.sitemaps.org/schemas/sitemap/0.9\">\n")
+		buf.WriteString("  <url><loc>https://toolbox.pengzhan.dev/</loc><priority>1.0</priority></url>\n")
+
+		// 动态根据注册的工具生成路由
+		for id := range base.Registry {
+			fmt.Fprintf(&buf, "  <url><loc>https://toolbox.pengzhan.dev/%s</loc><priority>0.8</priority></url>\n", id)
+		}
+		buf.WriteString("</urlset>")
+		c.Data(http.StatusOK, "application/xml; charset=utf-8", buf.Bytes())
+	})
 	// 3. 模板引擎初始化
 	// 递归加载 web 目录下所有的 .html 文件
 	tmpl, err := template.ParseFS(subFS, "layout.html", "index.html", "tools/*.html")
@@ -65,11 +83,32 @@ func main() {
 
 	// 通用页面渲染函数
 	serveIndex := func(c *gin.Context) {
-		data := gin.H{
-			"Title": "Own-Tools",
-			"GA_ID": gaID,
-		}
+		path := c.Request.URL.Path
+		title := "探索工具箱"
+		desc := "基于 Go 语言构建的模块化个人工具箱，提供汉字字帖生成、数字学习等多种实用生产力工具。"
+		keywords := "个人工具箱, 汉字字帖生成, 书法练习, 数字学习, Own-Tools"
+		baseURL := "https://toolbox.pengzhan.dev"
+		canonical := baseURL + path
+		                // 针对不同路径设置 SEO 标签
+		                switch path {
+		                case "/zitie":
+		                        title = "汉字字帖生成器 - 教学方格与步进式分解"
+		                        desc = "在线生成 2x3 教学方格字帖和 9 列步进式笔顺分解字帖，支持多种书法字体和古风排版。"
+		                        keywords = "字帖生成, 笔顺分解, 汉字教学, 书法字帖, 练字"
+		                case "/learn-number":
+		                        title = "趣味数字学习工具"
+		                        desc = "为儿童设计的数字学习与计数练习工具，生动活泼，寓教于乐。"
+		                        keywords = "数字学习, 儿童计数, 幼小衔接"
+		                }
 		
+		data := gin.H{
+			"Title":        title,
+			"Description":  desc,
+			"Keywords":     keywords,
+			"CanonicalURL": canonical,
+			"GA_ID":        gaID,
+		}
+
 		var buf bytes.Buffer
 		// 因为已经 Sub 了，模板名就是文件名
 		if err := tmpl.ExecuteTemplate(&buf, "layout.html", data); err != nil {
@@ -78,12 +117,13 @@ func main() {
 		}
 		c.Data(http.StatusOK, "text/html; charset=utf-8", buf.Bytes())
 	}
-
 	r.GET("/", serveIndex)
 	r.GET("/api/tools", func(c *gin.Context) {
 		var list []map[string]string
 		ids := make([]string, 0, len(base.Registry))
-		for id := range base.Registry { ids = append(ids, id) }
+		for id := range base.Registry {
+			ids = append(ids, id)
+		}
 		sort.Strings(ids)
 
 		for _, id := range ids {