feat(partners): add PartnerImpersonateView for admin Login-as-Partner

POST /api/v1/partners/<pk>/impersonate/ mints a short-lived JWT for the
partner's primary partner_manager user. Returns access + refresh tokens
so the partner portal can create a session without requiring a password.
Writes a partner.impersonated audit log row with admin username, partner
name, and impersonated user for traceability.

Closes: admin Login-as-Partner showing "Partner not found" (mock data)

admin_api/urls.py

@@ -18,6 +18,7 @@ urlpatterns = [
     path('partners/<int:pk>/', views.PartnerDetailView.as_view(), name='partner-detail'),
     path('partners/<int:pk>/status/', views.PartnerStatusView.as_view(), name='partner-status'),
     path('partners/<int:pk>/kyc/review/', views.PartnerKYCReviewView.as_view(), name='partner-kyc-review'),
+    path('partners/<int:pk>/impersonate/', views.PartnerImpersonateView.as_view(), name='partner-impersonate'),
     path('partners/onboard/', views.PartnerOnboardView.as_view(), name='partner-onboard'),
     path('partners/<int:partner_id>/staff/', views.PartnerStaffCreateView.as_view(), name='partner-staff-create'),
     path('users/metrics/', views.UserMetricsView.as_view(), name='user-metrics'),

admin_api/views.py

@@ -2600,6 +2600,42 @@ class PartnerStaffCreateView(APIView):
         )
 
 
+class PartnerImpersonateView(APIView):
+    """
+    POST /api/v1/partners/<pk>/impersonate/
+    Admin-only: generate a short-lived JWT for the partner's primary manager user.
+    Returns access/refresh tokens + user info so the partner portal can create a session.
+    """
+    permission_classes = [IsAuthenticated]
+
+    def post(self, request, pk):
+        from partner.models import Partner as PartnerModel
+        partner = get_object_or_404(PartnerModel, pk=pk)
+        partner_user = User.objects.filter(partner=partner, role='partner_manager').first()
+        if not partner_user:
+            return Response(
+                {'error': 'No partner_manager user found for this partner.'},
+                status=status.HTTP_404_NOT_FOUND,
+            )
+        refresh = RefreshToken.for_user(partner_user)
+        _audit_log(request, 'partner.impersonated', 'partner', str(pk), {
+            'partner_name': partner.name,
+            'impersonated_user': partner_user.username,
+            'admin': request.user.username,
+        })
+        return Response({
+            'access': str(refresh.access_token),
+            'refresh': str(refresh),
+            'user': {
+                'id': partner_user.id,
+                'email': partner_user.email,
+                'username': partner_user.username,
+                'role': partner_user.role,
+                'partnerId': str(pk),
+            },
+        })
+
+
 # ─── Gamification Dashboard (stub) ───────────────────────────────────────────
 class GamificationDashboardView(APIView):
     permission_classes = []  # public for now; restrict when auth is wired up