feat(notifications): proactively ask the browser for popup permission

Previously desktop popups had to be enabled from Settings. Now a dismissible
prompt card appears for signed-in users on a supporting browser that haven't
decided yet ("Turn on notifications?" + Enable/Later). Tapping Enable triggers
the browser permission request (user gesture, as browsers require), turns on
desktop popups, and immediately fires one (force) so the user sees it works.
Shown once per device (remembered in localStorage); mounted on both the
dashboard and POS/queue layouts. fa/en/ar added.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/dashboard/messages/en.json

@@ -1361,7 +1361,10 @@
       "tabBadge": "Unread count on the browser tab",
       "tabBadgeHint": "Shows the number of unread notifications in the tab title and favicon.",
       "toast": "In-app toast",
-      "toastHint": "Show a small banner inside the dashboard for new notifications."
+      "toastHint": "Show a small banner inside the dashboard for new notifications.",
+      "promptTitle": "Turn on notifications?",
+      "promptBody": "Get a popup + sound for new orders and waiter calls — even when this tab is in the background.",
+      "later": "Later"
     },
     "customRoles": {
       "title": "Custom Roles",