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/server.go

@@ -264,6 +264,8 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		s.settingsHandler(w, r)
 	case path == "/storage" && r.Method == http.MethodGet:
 		s.storagePageHandler(w, r)
+	case path == "/storage/network" && r.Method == http.MethodGet:
+		s.storageNetworkPageHandler(w, r)
 	case path == "/settings/notifications" && r.Method == http.MethodGet:
 		s.settingsNotificationsPageHandler(w, r)
 	case path == "/settings/security" && r.Method == http.MethodGet: