jmri: install xpra from upstream repo (v6.x, replaces Ubuntu v3.x)

Ubuntu 24.04 packages xpra 3.1.5 which is wire-incompatible with the
v6.x macOS client from xpra.org. Add xpra.org apt repo and install
current stable release so client and server versions match.

ansible/roles/jmri/tasks/main.yml

@@ -301,11 +301,31 @@
     path: "{{ jmri_home }}/.vnc"
     state: absent
 
-- name: Install Xpra
+- name: Remove Ubuntu-packaged xpra (too old — v3.x, incompatible with v6 client)
   ansible.builtin.apt:
     name: xpra
-    state: present
+    state: absent
-    update_cache: false
+
+- name: Install xpra.org apt signing key
+  ansible.builtin.get_url:
+    url: https://xpra.org/gpg.asc
+    dest: /usr/share/keyrings/xpra.asc
+    mode: '0644'
+
+- name: Add xpra.org upstream apt repository
+  ansible.builtin.copy:
+    dest: /etc/apt/sources.list.d/xpra.list
+    owner: root
+    group: root
+    mode: '0644'
+    content: |
+      deb [arch=amd64 signed-by=/usr/share/keyrings/xpra.asc] https://xpra.org/ noble main
+
+- name: Install Xpra from upstream repo (v6.x)
+  ansible.builtin.apt:
+    name: xpra
+    state: latest
+    update_cache: true
 
 - name: Deploy jmri-xpra systemd unit
   ansible.builtin.template: