storage IA: split /storage into Meghajtók + /storage/network (NAS)

User feedback on D1: the NAS-add button and the local-drive enrollment
buttons sat side by side with no separation — two different storage
classes interleaved on one page. Now two subpages under Tárhely:

- /storage — Tárhely — Meghajtók: physical drive registry, migrate,
  wizard entry points (Új meghajtó inicializálása / Meglévő meghajtó
  csatolása), unified agent view, manual add. The enrollment buttons
  now live unambiguously in the local-drive context.
- /storage/network — Tárhely — Hálózati tárhely (NAS): the NAS share
  list (NAS-megosztások) + add form + its JS (moved verbatim, incl.
  its own openDialog copy for the remove overlay).
- layout.html: Tárhely main-nav item gains two always-visible nested
  sub-links (Meghajtók / Hálózati tárhely, .nav-links-nested CSS);
  parent stays highlighted on both.
- handlers.go: NetworkStoragePaths moves out of storagePageData into
  the new networkStoragePageData (page key storage-network) +
  storageNetworkPageHandler; GET /storage/network route.
- Tests: /storage must NOT render the NAS section, /storage/network
  renders it and nothing drive-related; inventory + no-native-confirm
  scans cover the new template. Both template gates green.

controller/internal/web/templates/layout.html

@@ -23,7 +23,12 @@
         <ul class="nav-links">
             <li><a href="/" class="{{if eq .Page "dashboard"}}active{{end}}"><svg class="ico"><use href="#i-layout-grid"/></svg>Vezérlőpult</a></li>
             <li><a href="/stacks" class="{{if eq .Page "stacks"}}active{{end}}"><svg class="ico"><use href="#i-cloud"/></svg>Alkalmazások</a></li>
-            <li><a href="/storage" class="{{if eq .Page "storage"}}active{{end}}"><svg class="ico"><use href="#i-hard-drive"/></svg>Tárhely</a></li>
+            <li><a href="/storage" class="{{if or (eq .Page "storage") (eq .Page "storage-network")}}active{{end}}"><svg class="ico"><use href="#i-hard-drive"/></svg>Tárhely</a>
+                <ul class="nav-links nav-links-sub nav-links-nested">
+                    <li><a href="/storage" class="{{if eq .Page "storage"}}active{{end}}">Meghajtók</a></li>
+                    <li><a href="/storage/network" class="{{if eq .Page "storage-network"}}active{{end}}">Hálózati tárhely</a></li>
+                </ul>
+            </li>
             <li><a href="/backups" class="{{if eq .Page "backups"}}active{{end}}"><svg class="ico"><use href="#i-shield"/></svg>Biztonsági mentés</a></li>
             <li><a href="/monitoring" class="{{if eq .Page "monitoring"}}active{{end}}"><svg class="ico"><use href="#i-cpu"/></svg>Rendszermonitor</a></li>
             {{if .DebugMode}}<li><a href="/debug" class="{{if eq .Page "debug"}}active{{end}}"><svg class="ico"><use href="#i-wrench"/></svg>Debug</a></li>{{end}}