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/playbooks/day1_deploy_honcho.yml

@@ -2,13 +2,11 @@
 # ============================================================================
 # day1_deploy_honcho.yml
 # ----------------------------------------------------------------------------
-# Deploys Honcho + pgvector PostgreSQL on the `lincoln` host. Run AFTER
-# day0_linux_baseline.yml has been applied to the target.
+# Deploys Honcho + pgvector PostgreSQL on the `lincoln` host. Assumes day0
+# host provisioning (linux-baseline + expand_root_lv) is already complete.
 #
-# expand_root_lv runs first to reclaim any unallocated space left by the
-# Ubuntu autoinstall template (half-disk LV pattern).
-#
-# Usage:
+# Run via:
+#   ansible-playbook -i inventory.yml playbooks/day0_provision.yml -e target=lincoln
 #   ansible-playbook -i inventory.yml playbooks/day1_deploy_honcho.yml
 # ============================================================================
 
@@ -17,5 +15,4 @@
   become: true
   gather_facts: true
   roles:
-    - expand_root_lv
     - honcho