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/style.css

@@ -3240,3 +3240,16 @@ span.mono, .mono { font-family: var(--font-data); }
     padding: .5rem 1.5rem .5rem 1.75rem;
     font-size: .88rem;
 }
+
+/* Nested sub-links under a main-nav item (Tárhely → Meghajtók / Hálózati tárhely). */
+.nav-links-nested {
+    padding: 0;
+    list-style: none;
+}
+.nav-links-nested a {
+    padding: .4rem 1.5rem .4rem 3.1rem;
+    font-size: .85rem;
+}
+.nav-links-nested a.active {
+    border-left: 3px solid var(--blue);
+}