Add path=c:\ to autoexec for DOS extender findability

When the main executable is in a subdirectory but DOS4GW.EXE (or other
DOS extender) is at the ZIP root, DOS/4GW fails with 'No such file or
directory' because it only searches the current directory and PATH.
Adding 'path=c:\' before the 'cd' command ensures root-level DOS
extenders are always findable regardless of where the game EXE lives.

src/main/java/com/dostalgia/UploadResource.java

@@ -488,15 +488,19 @@ public class UploadResource {
     }
 
     private byte[] buildJsdosJson(String relExe) {
-        // DOS uses \ as path separator; / is a switch character.
+        // DOS uses \\ as path separator; / is a switch character.
         // If the executable is in a subdirectory, cd into it first.
         var parts = splitDirExe(relExe);
-        String script = parts[0] != null
-            ? "cd " + parts[0] + "\n" + parts[1]
-            : relExe;
+        StringBuilder script = new StringBuilder();
+        if (parts[0] != null) {
+            // Set PATH to include root so DOS extenders (DOS4GW etc.) are findable
+            script.append("path=c:\\\n");
+            script.append("cd ").append(parts[0]).append("\n");
+        }
+        script.append(parts[1]);
         String json = "{"
             + "\"autoexec\":{"
-            + "\"options\":{\"script\":{\"value\":\"" + escapeJson(script) + "\"}}"
+            + "\"options\":{\"script\":{\"value\":\"" + escapeJson(script.toString()) + "\"}}"
             + "},"
             + "\"output\":{"
             + "\"options\":{\"autolock\":{\"value\":true}}}"
@@ -539,8 +543,8 @@ public class UploadResource {
         sb.append("@echo off\n");
         sb.append("mount c .\n");
         sb.append("c:\n");
-        sb.append("cls\n");
         if (dir != null) {
+            sb.append("path=c:\\\n");
             sb.append("cd ").append(dir).append("\n");
         }
         sb.append(exe).append("\n");