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/metallb/Chart.yaml

@@ -5,7 +5,7 @@
 # exists at this path, resolves the dependency, and syncs the combined
 # rendered output as one Application — exactly like any other app in
 # apps/. This is the real, working example of the Helm-based app pattern
-# mentioned in docs/07-adding-new-apps.md: use it as a template if you want
+# mentioned in docs/08-adding-new-apps.md: use it as a template if you want
 # to bring in another third-party chart later.
 apiVersion: v2
 name: metallb-app