fix: Blood setup crash caused by Windows NE executable

Two bugs:

1. PlatformDetector buffer was 512 bytes — too small to read the NE
   header at offset 0x0E00 in Blood's SETUP.EXE. Increased to 4096
   bytes (0x1000), covering headers up to ~4KB.

2. findSetup() had no platform awareness — it picked SETUP.EXE
   (Windows 3.x NE executable) over SETMAIN.EXE (actual DOS4GW
   setup). Added platform detection to the sort, preferring DOS
   executables over Windows ones.
   Also added "setmain" to pattern list so Build engine games'
   DOS setup utilities are detected.

src/main/java/org/dostalgia/ExecutableDetector.java

@@ -82,9 +82,9 @@ public class ExecutableDetector {
     }
 
     public String findSetup(Path dir) throws IOException {
-        record Candidate(int depth, long size, String path) {}
+        record Candidate(int depth, boolean isWindows, long size, String path) {}
         List<Candidate> candidates = new ArrayList<>();
-        List<String> patterns = List.of("setup", "install", "config", "custom");
+        List<String> patterns = List.of("setup", "setmain", "install", "config", "custom");
 
         Files.walkFileTree(dir, new SimpleFileVisitor<>() {
             @Override
@@ -95,8 +95,9 @@ public class ExecutableDetector {
                     return FileVisitResult.CONTINUE;
                 for (String pat : patterns) {
                     if (stem.equals(pat) || stem.startsWith(pat + ".") || stem.startsWith(pat + "-")) {
+                        boolean isWin = "windows".equals(platform.detect(f));
                         candidates.add(new Candidate(
-                            f.getNameCount() - dir.getNameCount(), a.size(), f.toString()));
+                            f.getNameCount() - dir.getNameCount(), isWin, a.size(), f.toString()));
                         break;
                     }
                 }
@@ -105,7 +106,10 @@ public class ExecutableDetector {
         });
 
         if (candidates.isEmpty()) return null;
-        candidates.sort(Comparator.comparingInt(Candidate::depth).thenComparingLong(Candidate::size));
+        candidates.sort(Comparator
+            .<Candidate, Integer>comparingInt(c -> c.isWindows() ? 1 : 0)  // prefer DOS over Windows
+            .thenComparingInt(Candidate::depth)
+            .thenComparingLong(Candidate::size));
         return candidates.getFirst().path();
     }
 

src/main/java/org/dostalgia/PlatformDetector.java

@@ -30,7 +30,7 @@ public class PlatformDetector {
 
     /** Read enough PE header bytes from any InputStream (shared by Path and ZIP callers). */
     static byte[] readHeaderBytes(InputStream is) throws IOException {
-        byte[] buf = new byte[0x200];
+        byte[] buf = new byte[0x1000];
         int read = is.readNBytes(buf, 0, buf.length);
         return read < buf.length ? java.util.Arrays.copyOf(buf, read) : buf;
     }