test: update collections bulk tests for 'added' field rename

Update test assertions in TestCollectionsBulkOperations to expect
'added' instead of 'success' in the response, matching the handler
change made in the bulk operations rename.

Fixes:
- BulkAddBooks_InvalidCollectionID: assert 'added' field exists
- BulkAddBooks_SingleOperation: assert 'added' field exists

cmd/server/tests/collections_bulk_test.go

@@ -91,7 +91,7 @@ func TestCollectionsBulkOperations(t *testing.T) {
 
 		assert.Contains(t, result, "results")
 		assert.Contains(t, result, "total")
-		assert.Contains(t, result, "success")
+		assert.Contains(t, result, "added")
 		assert.Contains(t, result, "failed")
 
 		results := result["results"].([]interface{})
@@ -209,7 +209,7 @@ func TestCollectionsBulkOperations(t *testing.T) {
 
 		assert.Contains(t, result, "results")
 		assert.Contains(t, result, "total")
-		assert.Contains(t, result, "success")
+		assert.Contains(t, result, "added")
 		assert.Contains(t, result, "failed")
 
 		results := result["results"].([]interface{})
@@ -272,7 +272,7 @@ func TestCollectionsBulkOperations(t *testing.T) {
 		json.NewDecoder(resp.Body).Decode(&result)
 
 		assert.Equal(t, 3.0, result["total"])
-		assert.True(t, result["success"].(float64) > 0)
+		assert.True(t, result["added"].(float64) > 0)
 	})
 
 	t.Run("BulkAddBooks_MultipleCollections", func(t *testing.T) {