Remove the RepoISO integration; keep generic support for shares of other services

RepoISO now manages the NAS itself, so nasmon no longer polls it (settings field, dashboard card,
menu link and repoiso:* alerts are gone). Drop-in SMB includes, read-only listing and keeping
smbd/nfs-server running for other software's shares stay.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/web/templates/layout.html

@@ -16,7 +16,6 @@
     <a href="/shares" {{if eq .Page "shares"}}class="on"{{end}}>Shares</a>
     <a href="/alerts" {{if eq .Page "alerts"}}class="on"{{end}}>Alerts{{if .Alerts}} <span class="badge crit">{{.Alerts}}</span>{{end}}</a>
     <a href="/settings" {{if eq .Page "settings"}}class="on"{{end}}>Settings</a>
-    {{if .RepoISO}}<a href="{{.RepoISO}}" target="_blank" rel="noopener" title="ISO library, repositories, Proxmox exports">RepoISO ↗</a>{{end}}
   </nav>
   <span class="refresh" id="refresh-state" title="auto-refresh"></span>
 </header>