Ship Track C UX polish: toasts, settings, lists, navigation

Add a visible toast stack, fix presentError double-notify, wire density and auto-refresh settings, gate destructive confirms, improve empty/skeleton/search on resource lists, and enable browser history plus keyboard palette navigation.

client/errors.js

@@ -91,24 +91,16 @@ function stripPrefix(message) {
 }
 
 /**
- * Present error via toast + optional notification.
+ * Present error via toast (showAlert already writes the notification tray).
+ * Do not call notificationManager.add a second time — wrong signature and double noise.
  */
-export function presentError(err, method, { showAlert, notificationManager } = {}) {
+export function presentError(err, method, { showAlert } = {}) {
   const info = explainError(err, method)
   const text = `${info.title}: ${info.message}${info.recovery ? ` — ${info.recovery}` : ''}`
   if (typeof showAlert === 'function') {
-    showAlert(info.severity === 'warning' ? 'warning' : 'danger', text)
-  }
-  if (notificationManager?.add) {
-    try {
-      notificationManager.add({
-        type: info.severity === 'warning' ? 'warning' : 'error',
-        title: info.title,
-        message: info.message,
-      })
-    } catch {
-      // ignore
-    }
+    showAlert(info.severity === 'warning' ? 'warning' : 'danger', text, {
+      duration: 7000,
+    })
   }
   return info
 }