fix: resolve all integration test failures after storage layer refactor

- Use singleton container pattern for PostgreSQL + OpenSearch testcontainers
  (fixes container lifecycle issues with @TestInstance(PER_CLASS))
- Fix table name route_executions → executions in DetailControllerIT and
  ExecutionControllerIT
- Serialize processor headers as JSON (ObjectMapper) instead of Map.toString()
  for JSONB column compatibility
- Add nested mapping for processors field in OpenSearch index template
- Use .keyword sub-field for term queries on dynamically mapped text fields
- Add wildcard fallback queries for all text searches (substring matching)
- Isolate stats tests with unique route names to prevent data contamination
- Wait for OpenSearch indexing in SearchControllerIT with targeted Awaitility
- Reduce OpenSearch debounce to 100ms in test profile

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cameleer3-server-core/src/main/java/com/cameleer3/server/core/ingestion/IngestionService.java

@@ -8,13 +8,18 @@ import com.cameleer3.server.core.storage.ExecutionStore;
 import com.cameleer3.server.core.storage.ExecutionStore.ExecutionRecord;
 import com.cameleer3.server.core.storage.ExecutionStore.ProcessorRecord;
 import com.cameleer3.server.core.storage.model.MetricsSnapshot;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Map;
 import java.util.function.Consumer;
 
 public class IngestionService {
 
+    private static final ObjectMapper JSON = new ObjectMapper();
+
     private final ExecutionStore executionStore;
     private final DiagramStore diagramStore;
     private final WriteBuffer<MetricsSnapshot> metricsBuffer;
@@ -99,8 +104,7 @@ public class IngestionService {
                     p.getDurationMs(),
                     p.getErrorMessage(), p.getErrorStackTrace(),
                     truncateBody(p.getInputBody()), truncateBody(p.getOutputBody()),
-                    p.getInputHeaders() != null ? p.getInputHeaders().toString() : null,
-                    p.getOutputHeaders() != null ? p.getOutputHeaders().toString() : null
+                    toJson(p.getInputHeaders()), toJson(p.getOutputHeaders())
             ));
             if (p.getChildren() != null) {
                 flat.addAll(flattenProcessors(
@@ -116,4 +120,13 @@ public class IngestionService {
         if (body.length() > bodySizeLimit) return body.substring(0, bodySizeLimit);
         return body;
     }
+
+    private static String toJson(Map<String, String> headers) {
+        if (headers == null) return null;
+        try {
+            return JSON.writeValueAsString(headers);
+        } catch (JsonProcessingException e) {
+            return "{}";
+        }
+    }
 }