Move to a three-node cluster with a Talos VIP; add Longhorn

Every node is now both control plane and worker, giving real tolerance
for losing any single machine (etcd quorum needs 3, not 1). A Talos VIP
gives the cluster one stable address regardless of which node answers.

Also pre-installs Longhorn for replicated storage, backed by a Talos
UserVolume on each node's second disk (>=900GB, non-system) rather than
the default path — mirroring the pattern from the homescale repo.

Docs renumbered to make room for 06-longhorn.md; checklist, glossary,
network map, and CLAUDE.md's guided-bootstrap instructions updated to
match, including asking the user for node IPs, VIP, and disk info before
generating any Talos config.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/03-installing-argocd.md

@@ -46,7 +46,7 @@ each stage does:
 > **Ask Claude:** "why is a port-forward good enough for now, and what
 > would I need instead to reach this Argo CD from somewhere other than my
 > own machine?" — a preview of the Ingress topic in
-> [`docs/08-growing-up.md`](08-growing-up.md).
+> [`docs/09-growing-up.md`](09-growing-up.md).
 
 ## Checklist