fix(tasks): create the bashrc before sourcing a drop-in from it

The lineinfile task appends the source line to `~/.bashrc` but never declared `create`, so it aborted with "Destination
does not exist" whenever that file was missing. This hits every user configured with `create_home: false`, and it hit
every btrfs user as well, because their home is an empty subvolume and useradd therefore skips the skel rollout.

`mode` is added along with it, otherwise a newly created bashrc would inherit whatever the umask happens to be. The
existing `owner` and `group` were dead settings until now, since the file was never created by this task.

Co-authored-by: Copilot <copilot@github.com>

tasks/create_shell_rc_file.yaml

@@ -25,6 +25,8 @@
   ansible.builtin.lineinfile:
     path: "{{ _unix_users_home }}/.bashrc"
     line: "source \"{{ _shell_rc_file }}\""
+    create: true
     owner: "{{ unix_user.key }}"
     group: "{{ unix_user.value.group | default('users') }}"
+    mode: "0644"
     state: "present"