Add conditional restart support to client, bot, and bridge roles

For each of the 34 roles (3 clients, 9 bots, 22 bridges), this commit:
- Adds `_restart_necessary: false` default variable
- Adds `register:` directives to config/image/systemd tasks
- Computes `_restart_necessary` via set_fact (OR of all .changed results)
- Wires `(_restart_necessary | bool)` in group_vars/matrix_servers

This allows the systemd service manager to skip unnecessary restarts
when running install-* tags and nothing actually changed.

Service roles and complex multi-service roles will follow separately.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

roles/custom/matrix-bot-mjolnir/tasks/setup_install.yml

@@ -34,10 +34,10 @@
     force_source: "{{ matrix_bot_mjolnir_docker_image_force_pull if ansible_version.major > 2 or ansible_version.minor >= 8 else omit }}"
     force: "{{ omit if ansible_version.major > 2 or ansible_version.minor >= 8 else matrix_bot_mjolnir_docker_image_force_pull }}"
   when: "not matrix_bot_mjolnir_container_image_self_build | bool"
-  register: result
+  register: matrix_bot_mjolnir_container_image_pull_result
   retries: "{{ devture_playbook_help_container_retries_count }}"
   delay: "{{ devture_playbook_help_container_retries_delay }}"
-  until: result is not failed
+  until: matrix_bot_mjolnir_container_image_pull_result is not failed
 
 - name: Ensure mjolnir repository is present on self-build
   ansible.builtin.git:
@@ -68,6 +68,7 @@
     mode: 0644
     owner: "{{ matrix_user_name }}"
     group: "{{ matrix_group_name }}"
+  register: matrix_bot_mjolnir_config_result
 
 - name: Ensure matrix-bot-mjolnir container network is created
   community.general.docker_network:
@@ -83,6 +84,16 @@
     mode: 0644
   register: matrix_bot_mjolnir_systemd_service_result
 
+- name: Determine whether Mjolnir needs a restart
+  ansible.builtin.set_fact:
+    matrix_bot_mjolnir_restart_necessary: >-
+      {{
+        matrix_bot_mjolnir_migration_requires_restart | default(false)
+        or matrix_bot_mjolnir_config_result.changed | default(false)
+        or matrix_bot_mjolnir_systemd_service_result.changed | default(false)
+        or matrix_bot_mjolnir_container_image_pull_result.changed | default(false)
+      }}
+
 - name: Ensure matrix-bot-mjolnir.service restarted, if necessary
   ansible.builtin.service:
     name: "matrix-bot-mjolnir.service"