feat(expand_root_lv): new role to grow root LV to fill VG + resize fs

Reclaims the half-disk LV left by the Ubuntu Server autoinstall
template default. Idempotent — no-ops cleanly when there are no free PE
in the VG, and exits the play cleanly on hosts without LVM.

Supports ext4 and xfs. Does not handle partition resize (cloud-utils
growpart) — out of scope for the template fix-up case.

Wired into day1_deploy_honcho.yml ahead of the honcho role so newly
provisioned VMs get the fix-up automatically. Suitable to add to any
day1 playbook by simply listing it before the application role.

ansible/playbooks/day1_deploy_honcho.yml

@@ -5,6 +5,9 @@
 # Deploys Honcho + pgvector PostgreSQL on the `lincoln` host. Run AFTER
 # day0_linux_baseline.yml has been applied to the target.
 #
+# expand_root_lv runs first to reclaim any unallocated space left by the
+# Ubuntu autoinstall template (half-disk LV pattern).
+#
 # Usage:
 #   ansible-playbook -i inventory.yml playbooks/day1_deploy_honcho.yml
 # ============================================================================
@@ -14,4 +17,5 @@
   become: true
   gather_facts: true
   roles:
+    - expand_root_lv
     - honcho