test(02-01): add failing IngestionSchemaIT for new column population

- Tests processor tree metadata (depths, parent indexes)
- Tests exchange body concatenation for search
- Tests null snapshot graceful handling
- AbstractClickHouseIT loads 02-search-columns.sql
- DiagramRenderer/DiagramLayout stubs to fix pre-existing compilation error

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cameleer3-server-core/src/main/java/com/cameleer3/server/core/diagram/DiagramRenderer.java

@@ -3,26 +3,20 @@ package com.cameleer3.server.core.diagram;
 import com.cameleer3.common.graph.RouteGraph;
 
 /**
- * Renders route diagrams from {@link RouteGraph} definitions.
+ * Renders a route graph as SVG or as a positioned JSON layout.
  * <p>
- * Implementations produce either SVG documents for direct display or
- * JSON-serializable layout data for client-side rendering.
+ * Implementations handle layout computation and visual rendering.
+ * Stub interface -- full implementation in a later plan.
  */
 public interface DiagramRenderer {
 
     /**
-     * Render the route graph as an SVG XML document.
-     *
-     * @param graph the route graph definition
-     * @return SVG XML string
+     * Render the route graph as an SVG document string.
      */
     String renderSvg(RouteGraph graph);
 
     /**
-     * Compute the diagram layout with positioned nodes and edges.
-     *
-     * @param graph the route graph definition
-     * @return layout data suitable for JSON serialization
+     * Compute a positioned JSON layout for the route graph.
      */
     DiagramLayout layoutJson(RouteGraph graph);
 }