feat(kds): filter the kitchen display by station (kitchen / bar)

Complements the separate kitchen/bar printers with an on-screen split. The live
order DTO now carries each item's prep station (MenuItem → Category →
KitchenStation), and the KDS shows station tabs (All / Kitchen / Bar / …) that
appear only once ≥2 stations are in play. Selecting a station shows just the
tickets — and just the items within each ticket — for that station, so bar staff
see drinks and kitchen staff see food. Single-station cafés see the board
unchanged. fa/en/ar strings added.

Note: order status is still per-order (one advance button); the split is for
viewing/printing, not per-item status.

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

web/dashboard/messages/en.json

@@ -750,6 +750,8 @@
     "loading": "Loading...",
     "live": "Live",
     "polling": "Polling",
+    "allStations": "All",
+    "defaultStation": "Kitchen",
     "advance": "Next step",
     "status": {
       "Pending": "Pending",