fix(Core): sanitize uploader filenames and strip protocols

Stripping protocols (https, ftp, etc.) and replacing invalid filesystem characters with underscores. This prevents uploaders like Zipline from creating accidental subdirectories when saving .sxcu files.

Author: BrycensRanch

SnapX.Core/Upload/Custom/CustomUploaderItem.cs

@@ -148,7 +148,7 @@ public CustomUploaderItem()
     //     };
     // }
 
-    public override string? ToString()
+    public override string ToString()
     {
         if (!string.IsNullOrEmpty(Name))
         {
@@ -165,9 +165,28 @@ public CustomUploaderItem()
         return "Name";
     }
 
+    private static readonly string[] Protocols =
+    [
+        "https://", "http://", "ftp://", "sftp://", "ftps://",
+        "smb://", "afp://", "nfs://", "ssh://", "dav://", "davs://"
+    ];
     public string GetFileName()
     {
-        return ToString() + ".sxcu";
+        var name = ToString();
+
+        foreach (var protocol in Protocols)
+        {
+            var index = name.IndexOf(protocol, StringComparison.OrdinalIgnoreCase);
+            if (index != -1)
+            {
+                name = name.Remove(index, protocol.Length);
+            }
+        }
+
+        var invalid = Path.GetInvalidFileNameChars();
+        name = invalid.Aggregate(name, (current, c) => current.Replace(c, '_'));
+
+        return name + ".sxcu";
     }
 
     public string? GetRequestURL(CustomUploaderInput input)