feat: add OpenSearch highlight snippets to search results

- Add highlight field to ExecutionSummary record
- Request highlight fragments from OpenSearch when full-text search is active
- Pass matchContext to command palette for display

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

cameleer3-server-app/src/main/java/com/cameleer3/server/app/search/OpenSearchIndex.java

@@ -125,6 +125,10 @@ public class OpenSearchIndex implements SearchIndex {
         }
     }
 
+    private static final List<String> HIGHLIGHT_FIELDS = List.of(
+            "error_message", "processors.input_body", "processors.output_body",
+            "processors.input_headers", "processors.output_headers");
+
     private org.opensearch.client.opensearch.core.SearchRequest buildSearchRequest(
             SearchRequest request, int size) {
         return org.opensearch.client.opensearch.core.SearchRequest.of(b -> {
@@ -137,6 +141,17 @@ public class OpenSearchIndex implements SearchIndex {
                      .field(request.sortColumn())
                      .order("asc".equalsIgnoreCase(request.sortDir())
                              ? SortOrder.Asc : SortOrder.Desc)));
+            // Add highlight when full-text search is active
+            if (request.text() != null && !request.text().isBlank()) {
+                b.highlight(h -> {
+                    for (String field : HIGHLIGHT_FIELDS) {
+                        h.fields(field, hf -> hf
+                                .fragmentSize(120)
+                                .numberOfFragments(1));
+                    }
+                    return h;
+                });
+            }
             return b;
         });
     }
@@ -332,7 +347,18 @@ public class OpenSearchIndex implements SearchIndex {
                 src.get("duration_ms") != null ? ((Number) src.get("duration_ms")).longValue() : 0L,
                 (String) src.get("correlation_id"),
                 (String) src.get("error_message"),
-                null // diagramContentHash not stored in index
+                null, // diagramContentHash not stored in index
+                extractHighlight(hit)
         );
     }
+
+    private String extractHighlight(Hit<Map> hit) {
+        if (hit.highlight() == null || hit.highlight().isEmpty()) return null;
+        for (List<String> fragments : hit.highlight().values()) {
+            if (fragments != null && !fragments.isEmpty()) {
+                return fragments.get(0);
+            }
+        }
+        return null;
+    }
 }