feat(ui): agent-outdated banner on the NAS settings page (capability gate, Part 3)

- networkStoragePageData threads NetAddSupport (yes/no/unknown) via the short-budget
  netAddSupport probe (2 s ctx + cache — a down agent cannot stall the page)
- storage_network.html: support=no replaces the add form with the Hungarian
  alert-warning banner; share list + remove render in every state; yes/unknown
  render the form unchanged; load-time JS guarded for the formless render
- T5 render test (banner/no-form on 'no', form on yes/unknown); red-proof RP5 run
  (conditional dropped → banner assertions fail) and reverted
- template_id_gate + emoji_gate green

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PSK5g6qYLknKj8u3QAFEr6

controller/internal/web/storage_network_template_test.go

@@ -15,6 +15,7 @@ func TestStorageNetworkTemplate_CanonicalClasses(t *testing.T) {
 	s.loadTemplates()
 	data := map[string]interface{}{
 		"Page": "storage-network", "Title": "Hálózati tárhely",
+		"NetAddSupport": "yes",
 		"NetworkStoragePaths": []networkStorageItem{
 			{Name: "media", Label: "NAS media", Protocol: "nfs", Server: "10.0.0.5", Export: "/srv/media", Path: "/mnt/felhom-drives/media", Health: "ok"},
 			{Name: "ghost", Label: "Árva megosztás: ghost", Protocol: "nfs", Server: "10.0.0.5", Export: "/srv/ghost", Path: "/mnt/felhom-drives/ghost", Health: "idle", Orphan: true},
@@ -54,3 +55,52 @@ func TestStorageNetworkTemplate_CanonicalClasses(t *testing.T) {
 		t.Error("remove action missing")
 	}
 }
+
+// --- T5 (Scenario D): capability banner replaces the add form on an old agent -------------------
+// Companion red-proof: drop the {{if eq .NetAddSupport "no"}} wrapper (always render the form) →
+// the banner-present + form-absent assertions on "no" fail.
+func TestStorageNetworkTemplate_AgentOutdatedBanner(t *testing.T) {
+	s := testServer(t)
+	s.loadTemplates()
+	render := func(support string) string {
+		t.Helper()
+		var buf bytes.Buffer
+		err := s.tmpl.ExecuteTemplate(&buf, "storage_network", map[string]interface{}{
+			"Page": "storage-network", "Title": "Hálózati tárhely",
+			"NetAddSupport": support,
+			"NetworkStoragePaths": []networkStorageItem{
+				{Name: "media", Label: "NAS media", Protocol: "nfs", Server: "10.0.0.5", Export: "/srv/media", Path: "/mnt/felhom-drives/media", Health: "ok"},
+			},
+		})
+		if err != nil {
+			t.Fatalf("render (support=%s): %v", support, err)
+		}
+		return buf.String()
+	}
+
+	const banner = "A rendszer háttérszolgáltatása (ügynök) régebbi verziójú"
+	t.Run("no → banner instead of form; list + remove intact", func(t *testing.T) {
+		html := render("no")
+		if !strings.Contains(html, banner) {
+			t.Error("the §Part-3 banner is missing on an old agent")
+		}
+		if strings.Contains(html, `id="ns-add-form"`) {
+			t.Error("the add form must NOT render on an old agent")
+		}
+		// The share list + remove action stay fully usable in every state.
+		if !strings.Contains(html, "NAS media") || !strings.Contains(html, "Eltávolítás") {
+			t.Error("share list/remove must still render under the banner")
+		}
+	})
+	for _, support := range []string{"yes", "unknown"} {
+		t.Run(support+" → form as today", func(t *testing.T) {
+			html := render(support)
+			if !strings.Contains(html, `id="ns-add-form"`) {
+				t.Errorf("the add form must render on support=%s", support)
+			}
+			if strings.Contains(html, banner) {
+				t.Errorf("the banner must NOT render on support=%s", support)
+			}
+		})
+	}
+}