Fix remaining ansible-lint violations: file permissions, var-naming, package pinning

- risky-file-permissions (32): add explicit mode: to copy/template/file tasks,
  matching the umask-derived permissions they already had (0644 for configs
  and systemd units, 0755 for created directories) — no functional change.
- var-naming (28): prefix role-scoped vars with their role name across
  pi_dhtsensor, pi_dhtsensor_circuitpython, pi_shairport, pi_squeezelite,
  pi_squeezelite_custom, pi_sispmctl, pi_standard_setup, and pi_sysdweb's
  sysdweb_name (shared by 9 consuming roles). Updated every dependent
  template, task reference, and matching inventory.yml override, and
  verified resolved values with ansible-inventory before/after.
- Fixes a latent bug found while renaming: pi_standard_setup's "Get/Change
  WiFi country" tasks reused the name wifi_country for both the role default
  and a register, so the register silently clobbered the default before
  do_wifi_country ever read it. Split into distinct names so the intended
  default value is used.
- package-latest (2): pin docker-ce/docker-compose-plugin installs in
  server_debian_docker to state: present.
- no-handler (1): move pi_lirc's "Reboot if boot overlay changed" into a
  proper handler notified by the boot-overlay task.

ansible-lint now passes clean at the production profile.

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

roles/server_exthdd_mount/tasks/main.yml

@@ -3,14 +3,17 @@
   ansible.builtin.copy:
     src: media-passport4.mount
     dest: /etc/systemd/system
+    mode: "0644"
 - name: Automount passport5 systemd file
   ansible.builtin.copy:
     src: media-passport5.mount
     dest: /etc/systemd/system
+    mode: "0644"
 - name: Create udev rules
   ansible.builtin.copy:
     src: 99-automounts.rules
     dest: /etc/udev/rules.d
+    mode: "0644"
 - name: Systemd reread configs
   ansible.builtin.systemd:
     daemon_reload: true