Updated PLANS.md, AGENTS.md, and arabic-localization.md to reflect the “foundations now, full translations later” approach and marked progress accordingly.

Implemented localization foundations across backend and frontend (locale settings/middleware, preferred language, i18n wiring, RTL support, minimal Arabic UI strings, Accept-Language).
Added targeted backend and frontend tests plus a risks note for pending full translation coverage.

backend/apps/bookings/serializers.py

@@ -1,4 +1,5 @@
 from rest_framework import serializers
+from django.utils.translation import gettext_lazy as _
 
 from apps.bookings.models import Booking
 from apps.salons.models import Service, StaffProfile
@@ -46,7 +47,7 @@ class BookingCreateSerializer(serializers.ModelSerializer):
         service: Service = attrs["service"]
         staff = attrs.get("staff")
         if staff and staff.salon_id != service.salon_id:
-            raise serializers.ValidationError("Selected staff does not belong to this salon")
+            raise serializers.ValidationError(_("Selected staff does not belong to this salon"))
         return attrs
 
     def create(self, validated_data):