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-app/src/test/resources/application-test.yml

@@ -4,6 +4,7 @@ spring:
 
 opensearch:
   url: http://localhost:9200
+  debounce-ms: 100
 
 ingestion:
   buffer-capacity: 100