fix: Use mime.FormatMediaType for RFC 6266 compliant Content-Disposition (#7635)

Updated Content-Disposition header generation to use mime.FormatMediaType
from the standard library, which properly handles non-ASCII characters
and special characters per RFC 6266.

Changes:
- weed/server/common.go: Updated adjustHeaderContentDisposition to use
  mime.FormatMediaType instead of manual escaping with fileNameEscaper
- weed/operation/upload_content.go: Updated multipart form Content-Disposition
  to use mime.FormatMediaType
- weed/server/volume_server_handlers_read.go: Removed unused fileNameEscaper

This ensures correct filename display for international users across
filer downloads and file uploads.

Fixes #7634

weed/server/volume_server_handlers_read.go

@@ -34,8 +34,6 @@ import (
 
 const reqIsProxied = "proxied"
 
-var fileNameEscaper = strings.NewReplacer(`\`, `\\`, `"`, `\"`)
-
 func NotFound(w http.ResponseWriter) {
 	stats.VolumeServerHandlerCounter.WithLabelValues(stats.ErrorGetNotFound).Inc()
 	w.WriteHeader(http.StatusNotFound)