fix: expose exchange body in API, fix RouteFlow index mapping

Add inputBody/outputBody/inputHeaders/outputHeaders to ExecutionDetail
DTO so exchange-level bodies are returned by the detail endpoint. Show
"Exchange Input" and "Exchange Output" panels on the detail page when
the data is available.

Fix RouteFlow node click selecting the wrong processor snapshot by
building a flowToTreeIndex mapping that correctly translates flow
display index → diagram node index → processorId → processor tree
index. Previously the diagram node index was used directly as the
processor tree index, which broke when the two orderings differed.

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

cameleer3-server-core/src/main/java/com/cameleer3/server/core/detail/DetailService.java

@@ -25,7 +25,9 @@ public class DetailService {
                             exec.durationMs() != null ? exec.durationMs() : 0L,
                             exec.correlationId(), exec.exchangeId(),
                             exec.errorMessage(), exec.errorStacktrace(),
-                            exec.diagramContentHash(), roots
+                            exec.diagramContentHash(), roots,
+                            exec.inputBody(), exec.outputBody(),
+                            exec.inputHeaders(), exec.outputHeaders()
                     );
                 });
     }

cameleer3-server-core/src/main/java/com/cameleer3/server/core/detail/ExecutionDetail.java

@@ -22,6 +22,10 @@ import java.util.List;
  * @param errorStackTrace    error stack trace (empty string if no error)
  * @param diagramContentHash content hash linking to the active route diagram version
  * @param processors         nested processor execution tree (root nodes)
+ * @param inputBody          exchange input body at route entry (null if not captured)
+ * @param outputBody         exchange output body at route exit (null if not captured)
+ * @param inputHeaders       exchange input headers at route entry (null if not captured)
+ * @param outputHeaders      exchange output headers at route exit (null if not captured)
  */
 public record ExecutionDetail(
         String executionId,
@@ -37,6 +41,10 @@ public record ExecutionDetail(
         String errorMessage,
         String errorStackTrace,
         String diagramContentHash,
-        List<ProcessorNode> processors
+        List<ProcessorNode> processors,
+        String inputBody,
+        String outputBody,
+        String inputHeaders,
+        String outputHeaders
 ) {
 }