feat: keep and auto-mount CD images via imgmount instead of stripping

- Removed .iso, .cue, .img, .ccd from SKIP_EXT (they're now kept in bundles)
- Added CD_EXT set and findCdImages() method to detect mountable images
- buildDosboxConf() now generates imgmount D:/E:/… commands for each CD image
- Only .nrg, .mdf, .mds, .sub, .dmg are still stripped (unsupported formats)

Games with CD images will now work out of the box — DOSBox presents
them as CD-ROM drives and the game can find its disc.

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

@@ -380,13 +380,37 @@ public class UploadResource {
 
     // ─── Bundle Creation ─────────────────────────────────────────
 
-    /** File extensions that are never game data and should be excluded from .jsdos bundles. */
+    /** File extensions that are never game data and should be excluded from .jsdos bundles.
+     *  Only formats DOSBox can't mount natively are stripped.
+     *  Mountable formats (.iso, .cue, .img, .ccd) are kept and auto-mounted via imgmount. */
     private static final java.util.Set<String> SKIP_EXT = java.util.Set.of(
-        ".img", ".iso", ".nrg", ".mdf", ".mds",  // disk images
-        ".ccd", ".sub", ".cue",                   // CloneCD / CUE sheets
+        ".nrg", ".mdf", ".mds",  // disk images DOSBox can't mount natively
+        ".sub",                  // subchannel data (accompanies .ccd — CCD itself is kept)
         ".dmg"                   // Mac disk images
     );
 
+    /** File extensions that DOSBox can mount as CD-ROM via imgmount. */
+    private static final java.util.Set<String> CD_EXT = java.util.Set.of(
+        ".iso", ".cue", ".img", ".ccd"
+    );
+
+    /** Find mountable CD image files in the extracted game directory.
+     *  Returns relative paths (with forward slashes) sorted alphabetically. */
+    private List<String> findCdImages(Path dir) throws IOException {
+        List<String> cds = new ArrayList<>();
+        try (var walk = Files.walk(dir)) {
+            walk.filter(Files::isRegularFile).forEach(f -> {
+                String name = f.getFileName().toString().toLowerCase();
+                int dot = name.lastIndexOf('.');
+                if (dot >= 0 && CD_EXT.contains(name.substring(dot))) {
+                    cds.add(dir.relativize(f).toString().replace('\\', '/'));
+                }
+            });
+        }
+        cds.sort(String::compareTo);
+        return cds;
+    }
+
     /**
      * Executable filenames (lowercase, stem only, no extension) that should NEVER
      * be selected as the main game executable. These are DOS extenders, DPMI hosts,
@@ -415,7 +439,9 @@ public class UploadResource {
         Path jsdos = extractDir.resolve(".jsdos");
         Files.createDirectories(jsdos);
         String relExe = extractDir.relativize(Path.of(exePath)).toString();
-        Files.writeString(jsdos.resolve("dosbox.conf"), buildDosboxConf(relExe));
+        // Find CD images for DOSBox imgmount (mountable via D:, E:, …)
+        List<String> cdImages = findCdImages(extractDir);
+        Files.writeString(jsdos.resolve("dosbox.conf"), buildDosboxConf(relExe, cdImages));
         Files.write(jsdos.resolve("jsdos.json"), buildJsdosJson(relExe));
 
         // ZIP it up directly from extractDir (no temp copy)
@@ -524,8 +550,8 @@ public class UploadResource {
         return json.getBytes(java.nio.charset.StandardCharsets.UTF_8);
     }
 
-    private String buildDosboxConf(String relExe) {
-        // DOS uses \ as path separator; / is a switch character.
+    private String buildDosboxConf(String relExe, List<String> cdImages) {
+        // 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 dir = parts[0];
@@ -558,6 +584,12 @@ public class UploadResource {
         sb.append("[autoexec]\n");
         sb.append("@echo off\n");
         sb.append("mount c .\n");
+        // Mount CD images as D:, E:, … so games can find their CD
+        char driveLetter = 'D';
+        for (String img : cdImages) {
+            sb.append("imgmount ").append(driveLetter).append(" \"").append(img).append("\" -t cdrom\n");
+            driveLetter++;
+        }
         sb.append("c:\n");
         if (dir != null) {
             sb.append("path=c:\\\n");