chore(ui): polish empty states + sidebar icon + i18n page titles

- AppSidebar: switch the inbounds icon from UserOutlined (a single
  person — wrong semantic) to ImportOutlined, matching the empty-state
  icon and reflecting the actual concept of an incoming entry point.
- usePageTitle: stop hardcoding English titles; resolve them through
  i18n (menu.* keys are already translated), so the browser tab now
  follows the active language.
- InboundList / NodeList: replace the bare "—" empty cell with a
  centered icon + t('noData') message (ImportOutlined for inbounds,
  ClusterOutlined for nodes), and swap opacity:0.4 for
  var(--ant-color-text-secondary) so the text stays readable on the
  light theme's tinted card background.

frontend/src/pages/nodes/NodeList.css

@@ -135,6 +135,10 @@
 
 .card-empty {
   text-align: center;
-  opacity: 0.4;
-  padding: 20px 0;
+  color: var(--ant-color-text-secondary);
+  padding: 24px 12px;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 8px;
 }