feat: write leafs incrementally without rebuilding the graph.

Ladybug 0.19 stays FTS/HNSW queryable on MERGE of new ids; DROP INDEX
was the fatal path. bin/brain/add.go and POST /ingest land facts+info
in one transaction so watch/mail/git can become leafs now (Gitea #14).

internal/httpapi/mcp.go

@@ -144,7 +144,15 @@ func (s *Server) mcpCall(r *http.Request, params json.RawMessage) (any, error) {
 			return nil, fmt.Errorf("cancelled")
 		}
 		defer s.release()
-		body, err = s.api.Ingest(r.Context())
+		var payload []byte
+		text := strings.TrimSpace(fmt.Sprint(p.Arguments["text"]))
+		if text != "" && text != "<nil>" {
+			payload, err = json.Marshal(p.Arguments)
+			if err != nil {
+				return nil, err
+			}
+		}
+		body, err = s.api.Ingest(r.Context(), payload)
 	default:
 		return nil, fmt.Errorf("unknown tool %s", p.Name)
 	}