feat(day0): promote expand_root_lv to a canonical day0 step

The half-disk LV pattern affects ~90% of mk-labs VMs. Treating the
fix-up as application-specific (as it was in day1_deploy_honcho.yml)
means future deploys would each carry the same boilerplate, and any
day1 author could forget it.

This commit:

  * Adds playbooks/day0_expand_root_lv.yml — standalone day0 step,
    targets {{ target | default("all") }}, honors a per-host
    expand_root_lv_skip opt-out for multi-LV layouts.

  * Adds playbooks/day0_provision.yml — umbrella playbook chaining
    day0_linux_baseline + day0_expand_root_lv, so the operator runs
    ONE command per new VM.

  * Removes expand_root_lv from day1_deploy_honcho.yml — day0 is
    assumed complete before day1 begins (cleaner separation of
    concerns, matches the convention day1_deploy_semaphore already
    follows).

  * Updates the role README to document the lifecycle position and
    the opt-out flag for hosts with multi-LV plans.

ansible/roles/expand_root_lv/README.md

@@ -3,13 +3,26 @@
 Idempotent role that extends the root LVM logical volume to fill its
 volume group and grows the underlying filesystem (ext4 or xfs).
 
+## Where this runs in the lifecycle
+
+Part of the **day0** host-provisioning lifecycle. The canonical entry
+points are:
+
+```
+playbooks/day0_expand_root_lv.yml   # standalone
+playbooks/day0_provision.yml        # umbrella (baseline + expand_root_lv)
+```
+
+Day1 application-deploy playbooks should NOT include this role —
+day0 is assumed complete before day1 begins.
+
 ## 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.
+size — a longstanding installer default that surprises every operator
+who hasn't been bitten by it before. ~90% of mk-labs VMs need this
+fix-up before they're fully useful.
 
 ## Idempotency
 
@@ -17,41 +30,35 @@ needs this fix-up before it's fully useful.
   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
+- Safe to leave in a recurring playbook so future disk expansions
   (Proxmox-side disk grow → reboot → run role) are picked up
   automatically.
 
-## Usage
+## Opt-out for multi-LV hosts
 
-Standalone:
+If a host will have a **second logical volume in the same VG** (e.g. a
+dedicated `/var/lib/postgresql` LV for a database server), this role's
+"grow root to fill VG" behavior is wrong — it will consume the free PE
+that was being reserved for the second LV.
+
+Set in `host_vars/<host>.yml`:
 
 ```yaml
-- hosts: lincoln
-  become: true
-  roles:
-    - expand_root_lv
+expand_root_lv_skip: true
 ```
 
-Or chained ahead of an application role in a day1 playbook:
-
-```yaml
-- hosts: honcho_server
-  become: true
-  roles:
-    - expand_root_lv
-    - honcho
-```
+The day0 playbook checks this flag and skips the role cleanly.
 
 ## 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.             |
+| 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.
+Override the VG/LV names in `host_vars/<host>.yml` for hosts that use a
+different LVM layout.
 
 ## Limitations