Use distro release and Debian arch for the Docker apt repo

The repo line was hard-coded to bookworm/arm64 as a workaround before Docker published trixie packages. Derive it from ansible_distribution_release and map ansible_architecture to the Debian architecture name.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tasks/main.yml

@@ -24,9 +24,9 @@
     dest: /etc/apt/keyrings/docker.asc
     mode: '0644'
 
-- name: Add Docker repository for Debian 13 (use bookworm)
+- name: Add Docker repository
   apt_repository:
-    repo: "deb [arch=arm64 signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/debian bookworm stable"
+    repo: "deb [arch={{ docker_apt_arch[ansible_architecture] | default(ansible_architecture) }} signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/debian {{ ansible_distribution_release }} stable"
     state: present
     filename: docker
 

vars/main.yml

@@ -1 +1,5 @@
 ---
+# ansible_architecture -> Debian package architecture
+docker_apt_arch:
+  aarch64: arm64
+  x86_64: amd64