fix(handler): normalize root path to fix relative path performance

When root is configured as a relative path (e.g., "./lib/site/"),
filepath.Join normalizes it to "lib/site/" but the original value
was stored in h.root. This caused strings.TrimPrefix in serveFile
to fail, resulting in incorrect path calculations for GzipStatic.

The bug caused every request to attempt opening a non-existent
precompressed file path like "lib/site/lib/site/index.html.gz",
adding an extra failed os.Stat call per request and reducing
performance by ~50%.

Fix by normalizing root with filepath.Clean in NewStaticHandler
and SetRoot to ensure TrimPrefix works correctly.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/handler/static.go

@@ -82,8 +82,14 @@ type StaticHandler struct {
 //
 //	handler := handler.NewStaticHandler("/var/www", "/", []string{"index.html"}, true)
 func NewStaticHandler(root, pathPrefix string, index []string, useSendfile bool) *StaticHandler {
+	// 规范化 root 路径，确保 TrimPrefix 能正确工作
+	// filepath.Clean 会去掉 ./ 并规范化路径分隔符
+	cleanRoot := filepath.Clean(root)
+	if !strings.HasSuffix(cleanRoot, string(filepath.Separator)) {
+		cleanRoot += string(filepath.Separator)
+	}
 	return &StaticHandler{
-		root:        root,
+		root:        cleanRoot,
 		pathPrefix:  pathPrefix,
 		index:       index,
 		useSendfile: useSendfile,
@@ -136,8 +142,13 @@ func (h *StaticHandler) SetAlias(alias string) {
 // 参数：
 //   - root: 静态文件根目录
 func (h *StaticHandler) SetRoot(root string) {
-	h.root = root
+	// 规范化 root 路径
-	if root != "" {
+	cleanRoot := filepath.Clean(root)
+	if !strings.HasSuffix(cleanRoot, string(filepath.Separator)) {
+		cleanRoot += string(filepath.Separator)
+	}
+	h.root = cleanRoot
+	if cleanRoot != "" {
 		h.alias = ""
 	}
 }