fix(flatpak): bundle intltool for libdbusmenu build

intltool was removed from org.gnome.Sdk in 2019. libdbusmenu's configure
script requires it even with --disable-nls. Using cleanup: ["*"] ensures
intltool is only used at build time.

flatpak/com.ccswitch.desktop.yml

@@ -22,6 +22,15 @@ finish-args:
   - --filesystem=home
 
 modules:
+  # Required for libdbusmenu build (intltool was removed from GNOME SDK since 2019)
+  - name: intltool
+    cleanup:
+      - "*"
+    sources:
+      - type: archive
+        url: https://launchpad.net/intltool/trunk/0.51.0/+download/intltool-0.51.0.tar.gz
+        sha256: 67c74d94196b153b774ab9f89b2fa6c6ba79352407037c8c14d5aeb334e959cd
+
   # Required for tray icon support
   - name: libayatana-ido
     buildsystem: cmake-ninja