semantics: complete DEF-to-region migration, fix regressions

- Convert legacy [DEF🆔Type] anchors to #region/#endregion across 329 files
- Reinstate _normalize_timestamp_value in sql_generator.py
- Fix MarkerLogger→logger migration in events.py (molecular CoT markers)
- Fix dataset_review orchestrator dependencies (_build_execution_snapshot)
- Fix config_manager stale-record deletion (moved to save path only)
- Add 77 missing [/DEF:] closers in 5 unbalanced test files
- Update assistant_chat.integration.test.js for #region format
- Apply molecular-cot-logging markers (REASON/REFLECT/EXPLORE) via logger.* methods

backend/src/core/cot_logger.py

@@ -3,8 +3,8 @@
 #           Uses ContextVar for trace_id and span_id propagation across async contexts.
 #           Provides log(), MarkerLogger, seed_trace_id(), push_span(), pop_span().
 # @LAYER: Core
-# @RELATION: [CALLED_BY] -> [TraceContextMiddleware]
-# @RELATION: [CALLED_BY] -> [All C4+ service and route modules]
+# @RELATION CALLED_BY -> [TraceContextMiddleware]
+# @RELATION CALLED_BY -> [All C4+ service and route modules]
 # @PRE: Python 3.7+ (ContextVar available).
 # @POST: JSON log records written to the 'cot' logger at appropriate levels.
 # @SIDE_EFFECT: Writes structured JSON to the 'cot' Python logger.