test: add tests for platform assignment in user/vendor creation

Unit tests (test_admin_service.py):
- Vendor creation without platforms
- Vendor creation with single platform
- Vendor creation with multiple platforms
- Vendor creation with invalid platform ID (ignored)
- Vendor creation with duplicate code/subdomain (fails)
- Vendor creation with invalid company ID (fails)

Integration tests (test_vendors.py):
- Create vendor via API without platforms
- Create vendor via API with platforms
- Create vendor with duplicate code fails (409)
- Non-admin cannot create vendors (403)

Auth tests (test_auth.py):
- Super admin login includes is_super_admin=true
- Platform admin login includes is_super_admin=false
- Get current super admin info includes is_super_admin

Total: 69 admin platform tests passing

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/integration/api/v1/admin/test_auth.py

@@ -175,3 +175,48 @@ class TestAdminAuthAPI:
         assert response.status_code == 200
         data = response.json()
         assert data["message"] == "Logged out successfully"
+
+    def test_super_admin_login_includes_is_super_admin(
+        self, client, test_super_admin
+    ):
+        """Test super admin login includes is_super_admin in response."""
+        response = client.post(
+            "/api/v1/admin/auth/login",
+            json={
+                "email_or_username": test_super_admin.username,
+                "password": "superadminpass123",
+            },
+        )
+
+        assert response.status_code == 200
+        data = response.json()
+        assert "user" in data
+        assert "is_super_admin" in data["user"]
+        assert data["user"]["is_super_admin"] is True
+
+    def test_platform_admin_login_includes_is_super_admin(
+        self, client, test_platform_admin
+    ):
+        """Test platform admin login includes is_super_admin=False in response."""
+        response = client.post(
+            "/api/v1/admin/auth/login",
+            json={
+                "email_or_username": test_platform_admin.username,
+                "password": "platformadminpass123",
+            },
+        )
+
+        assert response.status_code == 200
+        data = response.json()
+        assert "user" in data
+        assert "is_super_admin" in data["user"]
+        assert data["user"]["is_super_admin"] is False
+
+    def test_get_current_super_admin_info(self, client, super_admin_headers, test_super_admin):
+        """Test getting current super admin user info includes is_super_admin."""
+        response = client.get("/api/v1/admin/auth/me", headers=super_admin_headers)
+
+        assert response.status_code == 200
+        data = response.json()
+        assert data["username"] == test_super_admin.username
+        assert data["is_super_admin"] is True