hub: shared host_detail_body sub-template + customer Host tab (v0.47.0 part 3)

- host_detail_body.html: {{define}}'d body sections extracted from
  host_detail.html; the standalone page is now chrome + the sub-template
- hosts.go: hostDetailData(host, r) view-model builder extracted from
  handleHostDetail (reused by both surfaces)
- store: ListHostsByCustomer (host_id order; the Host tab is a list by
  design - N hosts for a future HA cluster)
- customer Host tab renders one host_detail_body per host + cross-link;
  empty state when no host is enrolled
- tests: TestTemplates_CustomerHostTab(+_Empty), TestListHostsByCustomer

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Vvz1NCu22p8dGkRCpeX9re

hub/internal/web/templates/customer_unified.html

@@ -862,14 +862,21 @@
 
         </div>
 
-        <!-- ═══ Host ═══ -->
+        <!-- ═══ Host ═══ (a LIST by design — 1 host today, N for a later HA cluster) -->
         <div class="tab-panel" data-tab="host">
+        {{if .Hosts}}
+        {{range .Hosts}}
+        <p style="margin: 0 0 0.5rem;"><a href="/hosts/{{.HostID}}" class="back-link">Open host page: {{.HostID}} &rarr;</a></p>
+        {{template "host_detail_body" .}}
+        {{end}}
+        {{else}}
         <section class="card">
             <div class="empty-state" style="border: none;">
                 <p>No host enrolled yet.</p>
                 <p class="hint">A host appears here once it enrolls via the Day-0 bootstrap.</p>
             </div>
         </section>
+        {{end}}
         </div>
 
         <footer>