swap: add a swapfile role, 2 GB on asxpio-ops

The ops server has 3.7 GB RAM and no swap. Forgejo, MinIO and the apps
fit with room to spare, but a spike (a big push, git gc, parallel
image pulls) would OOM-kill a service instead of paging out.

swappiness 10, so it only swaps under real pressure.

Assisted-by: Claude:opus-5

ansible/playbooks/05-swap.yaml

@@ -0,0 +1,12 @@
+---
+# Swapfile on the ops server (3.7 GB RAM, no swap): Forgejo, MinIO and the
+# apps fit, but a spike would OOM-kill one of them instead of paging out.
+#
+# Usage:
+#   ansible-playbook playbooks/05-swap.yaml
+
+- name: Configure swap
+  hosts: ops_servers
+  become: true
+  roles:
+    - swap