Add xdsgui module: prebuilt binary + generate_XDS.INP from XDS wiki

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

xdsgui/build

@@ -0,0 +1,22 @@
+#!/usr/bin/env modbuild
+
+pbuild::prep() {
+    :
+}
+
+pbuild::configure() {
+    :
+}
+
+pbuild::compile() {
+    :
+}
+
+pbuild::install() {
+    # upstream ships unversioned binaries at fixed URLs; module version = download date
+    mkdir -p "${PREFIX}/bin"
+    cd "${PREFIX}/bin"
+    wget https://wiki.uni-konstanz.de/pub/linux_bin/xdsgui
+    wget https://wiki.uni-konstanz.de/pub/linux_bin/generate_XDS.INP
+    chmod a+x xdsgui generate_XDS.INP
+}