fix: normalize Windows backslash paths in weed admin file uploads (#7636)

fix: normalize Windows backslash paths in file uploads

When uploading files from a Windows client to a Linux server,
file paths containing backslashes were not being properly interpreted as
directory separators. This caused files intended for subdirectories to be
created in the root directory with backslashes in their filenames.

Changes:
- Add util.CleanWindowsPath and util.CleanWindowsPathBase helper functions
  in weed/util/fullpath.go for reusable path normalization
- Use path.Join/path.Clean/path.Base instead of filepath equivalents
  for URL path semantics (filepath is OS-specific)
- Apply normalization in weed admin handlers and filer upload parsing

Fixes #7628

weed/storage/needle/needle_parse_upload.go

@@ -128,7 +128,7 @@ func parseUpload(r *http.Request, sizeLimit int64, pu *ParsedUpload) (e error) {
 
 		pu.FileName = part.FileName()
 		if pu.FileName != "" {
-			pu.FileName = path.Base(pu.FileName)
+			pu.FileName = util.CleanWindowsPathBase(pu.FileName)
 		}
 
 		dataSize, e = pu.bytesBuffer.ReadFrom(io.LimitReader(part, sizeLimit+1))
@@ -169,7 +169,7 @@ func parseUpload(r *http.Request, sizeLimit int64, pu *ParsedUpload) (e error) {
 
 				// update
 				pu.Data = pu.bytesBuffer.Bytes()
-				pu.FileName = path.Base(fName)
+				pu.FileName = util.CleanWindowsPathBase(fName)
 				contentType = part.Header.Get("Content-Type")
 				part = part2
 				break
@@ -207,7 +207,7 @@ func parseUpload(r *http.Request, sizeLimit int64, pu *ParsedUpload) (e error) {
 		}
 
 		if pu.FileName != "" {
-			pu.FileName = path.Base(pu.FileName)
+			pu.FileName = util.CleanWindowsPathBase(pu.FileName)
 		} else {
 			pu.FileName = path.Base(r.URL.Path)
 		}