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/roles/expand_root_lv/README.md

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+# expand-root-lv role
+
+Idempotent role that extends the root LVM logical volume to fill its
+volume group and grows the underlying filesystem (ext4 or xfs).
+
+## Why this role exists
+
+The Ubuntu Server autoinstall template (used by the mk-labs `wed`-baked
+VM templates) provisions the root LV at roughly half the available disk
+size — a longstanding installer default that surprises everyone who
+hasn't been bitten by it before. Every freshly-provisioned VM in mk-labs
+needs this fix-up before it's fully useful.
+
+## Idempotency
+
+- If `vg_free_count == 0`, the `lvextend` step is skipped and the
+  filesystem-grow step is also skipped (nothing to resize against).
+- If the target volume group doesn't exist on the host (e.g. a non-LVM
+  layout), the role exits cleanly via `meta: end_play`.
+- Safe to leave in a day1 deploy playbook so future disk expansions
+  (Proxmox-side disk grow → reboot → run role) are picked up
+  automatically.
+
+## Usage
+
+Standalone:
+
+```yaml
+- hosts: lincoln
+  become: true
+  roles:
+    - expand_root_lv
+```
+
+Or chained ahead of an application role in a day1 playbook:
+
+```yaml
+- hosts: honcho_server
+  become: true
+  roles:
+    - expand_root_lv
+    - honcho
+```
+
+## Defaults
+
+| Variable                          | Default       | Purpose                                           |
+|-----------------------------------|---------------|---------------------------------------------------|
+| `expand_root_lv_vg_name`          | `ubuntu-vg`   | LVM volume group name (Ubuntu installer default). |
+| `expand_root_lv_lv_name`          | `ubuntu-lv`   | LVM logical volume name (Ubuntu installer default). |
+| `expand_root_lv_mountpoint`       | `/`           | Mountpoint of the filesystem to grow.             |
+
+Override these in `host_vars/<host>.yml` for hosts that use a different
+LVM layout. Hosts without LVM are silently no-op'd.
+
+## Limitations
+
+- Does not extend the underlying partition. If the operator grows the
+  Proxmox disk and the partition itself needs to grow before lvextend
+  can claim the new space, run `growpart /dev/sda 3` (or equivalent)
+  first. A future enhancement could automate this via `cloud-utils`'
+  `growpart` package, but it's out of scope for the initial template
+  fix-up case where the partition already covers the whole disk.