feat(base): Add snapper setup stack

Creates separate snapper services for root and home directories. Does
_not_ yet set up any btrfs mounts or ensure that they are mounted at the
locations.

books/void_base.yaml

@@ -131,3 +131,74 @@
         state: link
       with_items: [chronyd]
       listen: installed-chrony
+
+- name: Set up snapper backups
+  hosts: target_system
+  become: true
+  tags:
+    - btrfs
+    - snapshots
+  tasks:
+    - name: Install snapper
+      community.general.xbps:
+        name:
+          - snapper
+        state: present
+      notify: installed-snapper
+
+    # https://wiki.archlinux.org/title/Snapper#updatedb
+    - name: Disable updatedb indexing for snapshot directories
+      ansible.builtin.copy:
+        content: 'PRUNENAMES = ".snapshots"'
+        dest: "/etc/updatedb.conf"
+        owner: root
+        group: root
+        mode: 0644
+        force: true
+
+    - name: Ensure snapper configs directory exists
+      ansible.builtin.file:
+        dest: "/etc/snapper/configs"
+        state: directory
+        recurse: true
+
+    - name: Ensure root /.snapshots directory exists
+      ansible.builtin.file:
+        dest: "/.snapshots"
+        state: directory
+        mode: 0755
+
+    - name: Create root backup configuration
+      ansible.builtin.template:
+        src: snapper-configurations/root.j2
+        dest: "/etc/snapper/configs/root"
+        mode: 0640
+        force: true # ensure contents are always exact
+
+    - name: Ensure home /.snapshots directory exists
+      ansible.builtin.file:
+        dest: "/home/.snapshots"
+        state: directory
+        mode: 0755
+
+    - name: Create homedir backup configuration
+      ansible.builtin.template:
+        src: snapper-configurations/home.j2
+        dest: "/etc/snapper/configs/home"
+        mode: 0640
+        force: true
+
+  handlers:
+  #   # Do NOT activate the snapperd service -
+  #   # on systems without elogind I guess? Unsure
+  #   - name: Activate snapper service
+  #     ansible.builtin.file:
+  #       force: "yes"
+  #       src: "/etc/sv/snapperd"
+  #       dest: "/etc/runit/runsvdir/default/snapperd"
+  #       state: link
+  #     listen: installed-snapper
+    - name: Snapper handler stub
+      ansible.builtin.debug:
+        msg: ""
+      listen: installed-snapper