Fix ansible-lint violations: FQCN, formatting, bugs, role renames

- Auto-fix FQCN, YAML formatting, jinja spacing, and free-form module
  syntax via ansible-lint --fix
- Fix comments misplaced inside module args by the auto-fixer
  (bluetooth-monitor, pi_standard_setup, pi_musicmouse)
- Fix notify: references left stale (lowercase) after handler names
  were re-cased, which would have silently broken reboot/restart
  handlers (pi_disable_onboard_bluetooth, pi_hifiberry_amp,
  pi_squeezelite, pi_standard_setup)
- Fix a task in pis/debmatic-install.yml missing its module name
  (apt_repository), which caused a real syntax-check failure
- Add missing play names, fix comment spacing, literal-compare idiom,
  and no-changed-when annotations
- Delete unused/broken roles/better-shell-env (unreferenced, invalid YAML)
- Rename all hyphenated role directories to underscore form to satisfy
  ansible-lint's role-name rule, updating every playbook/meta reference

Remaining lint findings (var-naming, package-latest, risky-file-permissions,
no-handler) intentionally left for follow-up per user decision.

roles/server_debian_docker/README.md

@@ -0,0 +1,3 @@
+# server_debian_docker
+
+Installs Docker CE on Debian via the official Docker apt repository.

roles/server_debian_docker/tasks/main.yml

@@ -0,0 +1,37 @@
+---
+- name: Install required system packages
+  ansible.builtin.apt:
+    name:
+      - apt-transport-https
+      - ca-certificates
+      - curl
+      - software-properties-common
+      - python3-pip
+      - virtualenv
+      - python3-setuptools
+    state: latest
+    update_cache: true
+
+- name: Add Docker GPG apt Key
+  ansible.builtin.apt_key:
+    url: https://download.docker.com/linux/debian/gpg
+    state: present
+
+- name: Add Docker Repository
+  ansible.builtin.apt_repository:
+    repo: deb https://download.docker.com/linux/debian {{ ansible_facts['distribution_release'] }} stable
+    state: present
+
+- name: Update apt and install docker-ce
+  ansible.builtin.apt:
+    name:
+      - docker-ce
+      - docker-compose-plugin
+    state: latest
+    update_cache: true
+
+- name: Add core to docker group
+  ansible.builtin.user:
+    name: core
+    groups: docker
+    append: true