fix: 从源头解决下划线文件名问题并优化代码

- Vite配置chunkFileNames去除开头的下划线，避免Go embed/http.FS过滤
- 使用mime.TypeByExtension自动推断Content-Type，替代手动映射
- 移除调试日志（文件列表、全局中间件打印）

backend/cmd/main.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io/fs"
 	"log"
+	"mime"
 	"net/url"
 	"os"
 	"strings"
@@ -228,11 +229,6 @@ func startServer() {
 	r.Use(middleware.Recovery())
 	r.Use(middleware.Cors())
 
-	r.Use(func(c *gin.Context) {
-		fmt.Printf("全局中间件: %s %s\n", c.Request.Method, c.Request.URL.Path)
-		c.Next()
-	})
-
 	r.Static("/uploads", "uploads")
 	router.SetupRoutes(r)
 	setupEmbeddedFrontend(r)
@@ -255,17 +251,6 @@ func setupEmbeddedFrontend(r *gin.Engine) {
 		return
 	}
 
-	log.Printf("[Embed] Listing embedded files in assets/:")
-	fs.WalkDir(distFS, "assets", func(path string, d fs.DirEntry, err error) error {
-		if err != nil {
-			return err
-		}
-		if !d.IsDir() {
-			log.Printf("[Embed]   %s", path)
-		}
-		return nil
-	})
-
 	indexHTML, err := fs.ReadFile(distFS, "index.html")
 	if err != nil {
 		log.Printf("Warning: index.html not found in embedded dist")
@@ -284,36 +269,15 @@ func setupEmbeddedFrontend(r *gin.Engine) {
 
 		data, err := fs.ReadFile(distFS, fullPath)
 		if err != nil {
-			log.Printf("[Assets] File not found in embedded FS: %s, error: %v", fullPath, err)
 			c.Status(404)
 			return
 		}
 
-		contentType := "application/octet-stream"
-		switch {
-		case strings.HasSuffix(decodedPath, ".js"):
-			contentType = "application/javascript"
-		case strings.HasSuffix(decodedPath, ".css"):
-			contentType = "text/css"
-		case strings.HasSuffix(decodedPath, ".html"):
-			contentType = "text/html"
-		case strings.HasSuffix(decodedPath, ".json"):
-			contentType = "application/json"
-		case strings.HasSuffix(decodedPath, ".png"):
-			contentType = "image/png"
-		case strings.HasSuffix(decodedPath, ".jpg") || strings.HasSuffix(decodedPath, ".jpeg"):
-			contentType = "image/jpeg"
-		case strings.HasSuffix(decodedPath, ".svg"):
-			contentType = "image/svg+xml"
-		case strings.HasSuffix(decodedPath, ".ico"):
-			contentType = "image/x-icon"
-		case strings.HasSuffix(decodedPath, ".woff"):
-			contentType = "font/woff"
-		case strings.HasSuffix(decodedPath, ".woff2"):
-			contentType = "font/woff2"
+		contentType := mime.TypeByExtension(decodedPath)
+		if contentType == "" {
+			contentType = "application/octet-stream"
 		}
 
-		c.Header("Content-Type", contentType)
 		c.Header("Cache-Control", "public, max-age=31536000, immutable")
 		c.Data(200, contentType, data)
 	})
@@ -330,18 +294,9 @@ func setupEmbeddedFrontend(r *gin.Engine) {
 			decodedPath = path
 		}
 		if data, err := fs.ReadFile(distFS, decodedPath); err == nil {
-			contentType := "application/octet-stream"
-			switch {
-			case strings.HasSuffix(decodedPath, ".js"):
-				contentType = "application/javascript"
-			case strings.HasSuffix(decodedPath, ".css"):
-				contentType = "text/css"
-			case strings.HasSuffix(decodedPath, ".html"):
-				contentType = "text/html"
-			case strings.HasSuffix(decodedPath, ".png"):
-				contentType = "image/png"
-			case strings.HasSuffix(decodedPath, ".svg"):
-				contentType = "image/svg+xml"
+			contentType := mime.TypeByExtension(decodedPath)
+			if contentType == "" {
+				contentType = "application/octet-stream"
 			}
 			c.Data(200, contentType, data)
 			return