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/05-metallb.md

@@ -34,7 +34,7 @@ Helm chart that does two things at once (see
 
 - Pulls in the official upstream MetalLB chart as a dependency — this is
   also the real, working example of a Helm-based app mentioned in
-  [`docs/07-adding-new-apps.md`](07-adding-new-apps.md).
+  [`docs/08-adding-new-apps.md`](08-adding-new-apps.md).
 - Carries two templates of its own
   ([`apps/metallb/templates/`](../apps/metallb/templates)): an
   `IPAddressPool` and an `L2Advertisement` — MetalLB's own custom
@@ -152,4 +152,4 @@ the only place this address gets recorded at all.
 - [ ] `kubectl -n demo get svc demo` shows a real `EXTERNAL-IP`, page loads in a browser
 - [ ] `argocd-server` patched to `LoadBalancer`, reachable at its own address without port-forwarding
 
-Continue to [`docs/06-your-first-change.md`](06-your-first-change.md).
+Continue to [`docs/06-longhorn.md`](06-longhorn.md).