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>

apps/demo.yaml

@@ -16,7 +16,7 @@
 # (e.g. a database or ingress controller from a public chart repo). Argo CD
 # detects a Helm chart automatically when it finds a Chart.yaml at the
 # source path, resolves its dependencies, and syncs the rendered output just
-# like any other app. See docs/07-adding-new-apps.md for a worked example —
+# like any other app. See docs/08-adding-new-apps.md for a worked example —
 # the demo app deliberately stays plain manifests so the GitOps loop is easy
 # to read end to end with no templating in the way.
 apiVersion: argoproj.io/v1alpha1