ui(adminui): clusters pages — button groups, notice-alert tint, prose trim

Task 1 of the AdminUI UI sweep. Behavior-preserving: only wrappers, classes
and prose change — every @onclick, disabled, href and arm->confirm flow is
untouched.

Buttons -> Bootstrap btn-group:
- ClusterOverview page-head Edit cluster + Deployments pair
- Edit-form feet (Save+Cancel grouped; ms-auto Delete stays outside):
  ClusterEdit, NodeEdit, NewCluster, AclEdit
- ClusterRedundancy confirm-failover Confirm+Cancel (ms-2 dropped)
- AclEdit permission-bundle presets: btn-link + middot separators become an
  outline-secondary btn-group

Inline style="border-color:var(--alert)" (a no-op — that token is defined
nowhere) replaced by the .notice-alert class: NodeEdit, AclEdit, ClusterEdit.

Prose (unconditional documentation deleted; state banners/legends kept):
- ClusterRedundancy: removed the stale RedundancyStateActor "on each admin
  node" block (cluster-scoped singleton on driver nodes since mesh Phase 6)
  which also hyperlinked an unserved repo path; trimmed the mesh-split
  explanation to its data-provenance first sentence
- ClusterAcls: removed the Security:Acl:Enabled mode walkthrough and the
  grant/principal explanation (both in docs/security.md); kept the
  unresolved-chip decoder and trimmed the empty state to one sentence
- AclEdit: removed its near-duplicate of that walkthrough
- ClusterAudit: dropped the stale (F3) label and the EventId/CorrelationId
  dedup sentence; kept the page-size + Details-JSON caption
- ClusterNamespaces / NamespaceEdit: retired-in-v3 placeholders reworded to
  past tense — Batches 2/3 shipped, /raw and /uns are live

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Pages/Clusters/NamespaceEdit.razor

@@ -15,7 +15,7 @@
     <div style="padding:1rem">
         The <code>Namespace</code> entity has been removed. The v3 Raw/UNS split replaces it —
         raw driver folders and the unified namespace are managed on the <strong>/raw</strong> and
-        <strong>/uns</strong> pages, arriving in v3 Batch 2/3. This editor no longer applies.
+        <strong>/uns</strong> pages. This editor no longer applies.
     </div>
 </section>