feat: patch hardcoded absolute DOS paths in game configs during upload

Adds fixAbsoluteConfigPaths() which runs after flattening and cue fixing
during game upload. Detects known config files (FALLOUT.CFG, etc.) with
hardcoded C:\dir\ paths and rewrites them to .\ relative paths, so games
like Fallout can find their DAT files after flattening moves everything
to the bundle root.

Uses byte-level replacement to preserve original CRLF line endings and
encoding. Extensible via CONFIG_PATH_FIXES map — add new entries for
other games with the same problem.

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

@@ -87,6 +87,15 @@ public class UploadResource {
                 LOG.warning("Failed to fix cue references: " + e.getMessage());
             }
 
+            // Patch game config files with hardcoded absolute paths
+            // Some games (Fallout, etc.) have FALLOUT.CFG with C:\dir\ paths
+            // that break after flattening moves files to root.
+            try {
+                fixAbsoluteConfigPaths(extractDir);
+            } catch (Exception e) {
+                LOG.warning("Failed to patch config paths: " + e.getMessage());
+            }
+
             // Find main executable
             String mainExe = findMainExe(extractDir);
 
@@ -471,6 +480,74 @@ public class UploadResource {
         }
     }
 
+    /** Known game config files that may have hardcoded absolute DOS paths.
+     *  Key = filename pattern (lowercase), Value = list of path prefixes to
+     *  replace with ".\\" (relative to the game root). */
+    private static final java.util.Map<String, java.util.List<String>> CONFIG_PATH_FIXES =
+        java.util.Map.of(
+            "fallout.cfg", java.util.List.of("c:\\fallout1\\", "c:\\fallout2\\", "c:\\fallout\\")
+        );
+
+    /**
+     * Patch known game config files that contain hardcoded absolute DOS paths
+     * like {@code master_dat=C:\fallout1\master.dat}. After flattening moves
+     * everything to the bundle root, these paths break. Rewrites them to
+     * relative {@code .\master.dat} instead.
+     */
+    private static void fixAbsoluteConfigPaths(Path extractDir) throws IOException {
+        try (var walk = Files.walk(extractDir)) {
+            walk.filter(Files::isRegularFile).forEach(f -> {
+                String name = f.getFileName().toString().toLowerCase();
+                var prefixes = CONFIG_PATH_FIXES.get(name);
+                if (prefixes == null) return;
+                try {
+                    byte[] data = Files.readAllBytes(f);
+                    byte[] original = data.clone();
+                    for (String prefix : prefixes) {
+                        // Replace both "C:\dir\" and "c:\dir\" patterns
+                        byte[] pBytes = prefix.getBytes(java.nio.charset.StandardCharsets.ISO_8859_1);
+                        byte[] pSlash = prefix.replace('\\', '/')
+                            .getBytes(java.nio.charset.StandardCharsets.ISO_8859_1);
+                        byte[] rel = ".\\".getBytes(java.nio.charset.StandardCharsets.ISO_8859_1);
+                        byte[] relSlash = "./"
+                            .getBytes(java.nio.charset.StandardCharsets.ISO_8859_1);
+                        data = replaceBytes(data, pBytes, rel);
+                        data = replaceBytes(data, pSlash, relSlash);
+                    }
+                    if (!java.util.Arrays.equals(data, original)) {
+                        Files.write(f, data);
+                        LOG.info("Patched absolute paths in " + f.getFileName());
+                    }
+                } catch (IOException e) {
+                    LOG.warning("Failed to patch " + f.getFileName() + ": " + e.getMessage());
+                }
+            });
+        }
+    }
+
+    /** Simple byte-level search-and-replace (preserves CRLF, encoding, etc.). */
+    private static byte[] replaceBytes(byte[] src, byte[] search, byte[] replacement) {
+        if (search.length == 0) return src;
+        java.util.ArrayList<Byte> result = new java.util.ArrayList<>(src.length);
+        int i = 0;
+        while (i <= src.length - search.length) {
+            boolean match = true;
+            for (int j = 0; j < search.length; j++) {
+                if (src[i + j] != search[j]) { match = false; break; }
+            }
+            if (match) {
+                for (byte b : replacement) result.add(b);
+                i += search.length;
+            } else {
+                result.add(src[i++]);
+            }
+        }
+        while (i < src.length) result.add(src[i++]);
+        byte[] out = new byte[result.size()];
+        for (int k = 0; k < out.length; k++) out[k] = result.get(k);
+        return out;
+    }
+
     /** 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 {