Allow address.country and address.state as company sort fields.

Frontend sends nested address field names for sorting; accept them alongside the existing country and state aliases.

Co-authored-by: Cursor <cursoragent@cursor.com>

pkg/mongo/cursor_test.go

@@ -53,3 +53,29 @@ func TestHashFilterStable(t *testing.T) {
 		t.Fatalf("expected stable non-empty hash, got %q and %q", a, b)
 	}
 }
+
+func TestDocumentSortValueNestedField(t *testing.T) {
+	doc := bson.M{
+		"_id": bson.NewObjectID(),
+		"address": bson.M{
+			"country": "US",
+			"state":   "NY",
+		},
+	}
+
+	country, err := documentSortValue(doc, "address.country")
+	if err != nil {
+		t.Fatalf("address.country: %v", err)
+	}
+	if country != "US" {
+		t.Fatalf("expected US, got %v", country)
+	}
+
+	state, err := documentSortValue(doc, "address.state")
+	if err != nil {
+		t.Fatalf("address.state: %v", err)
+	}
+	if state != "NY" {
+		t.Fatalf("expected NY, got %v", state)
+	}
+}