feat: add query observability and collation safeguards

docs/API_INTEGRATION.md

@@ -267,6 +267,10 @@ GET  /api/knowledge/quality/assets/{assetId}/conflicts
 GET  /api/knowledge/quality/index-health
 GET  /api/knowledge/quality/metrics
 GET  /api/knowledge/quality/alerts?includeResolved=false&limit=100
+GET  /api/knowledge/quality/query-traces?status=&domain=&limit=50
+GET  /api/knowledge/quality/query-traces/{requestId}
+
+`query-traces` 仅返回租户内的结果摘要、候选通道/排序和证据使用状态，不返回原始问题、答案或附件正文；摘要字段由 `aihr_20260804_query_result_observability_mysql8.sql` 增量补齐。
 GET  /api/knowledge/quality/glossary?status=ACTIVE&limit=100
 POST /api/knowledge/quality/glossary
 POST /api/knowledge/quality/glossary/{id}/approve

docs/BRD_PRODUCTION_MIGRATION_RUNBOOK.md

@@ -155,6 +155,7 @@ mysql --default-character-set=utf8mb4 "$DB_NAME" < backend/script/sql/update/aih
 mysql --default-character-set=utf8mb4 "$DB_NAME" < backend/script/sql/update/aihr_20260802_data_quality_observability_mysql8.sql
 mysql --default-character-set=utf8mb4 "$DB_NAME" < backend/script/sql/update/aihr_20260803_data_quality_structure_mysql8.sql
 mysql --default-character-set=utf8mb4 "$DB_NAME" < backend/script/sql/update/aihr_20260804_data_quality_feedback_loop_mysql8.sql
+mysql --default-character-set=utf8mb4 "$DB_NAME" < backend/script/sql/update/aihr_20260804_unify_all_collations_mysql8.sql
 mysql --default-character-set=utf8mb4 "$DB_NAME" < backend/script/sql/update/aihr_20260802_feedback_question_bridge_mysql8.sql
 mysql --default-character-set=utf8mb4 "$DB_NAME" < backend/script/sql/update/aihr_20260805_knowledge_attachment_immutability_mysql8.sql
 mysql --default-character-set=utf8mb4 "$DB_NAME" < backend/script/sql/update/aihr_20260806_data_quality_extraction_evidence_mysql8.sql
@@ -167,6 +168,7 @@ mysql --default-character-set=utf8mb4 "$DB_NAME" < backend/script/sql/update/aih
 mysql --default-character-set=utf8mb4 "$DB_NAME" < backend/script/sql/update/aihr_20260813_golden_calibration_mysql8.sql
 mysql --default-character-set=utf8mb4 "$DB_NAME" < backend/script/sql/update/aihr_20260814_knowledge_privacy_derivative_mysql8.sql
 mysql --default-character-set=utf8mb4 "$DB_NAME" < backend/script/sql/update/aihr_20260815_rag_candidate_trace_mysql8.sql
+mysql --default-character-set=utf8mb4 "$DB_NAME" < backend/script/sql/update/aihr_20260804_query_result_observability_mysql8.sql
 mysql --default-character-set=utf8mb4 "$DB_NAME" < backend/script/sql/update/aihr_20260815_knowledge_rollout_compat_mysql8.sql
 mysql --default-character-set=utf8mb4 "$DB_NAME" < backend/script/sql/update/aihr_20260816_knowledge_version_pointers_mysql8.sql
 mysql --default-character-set=utf8mb4 "$DB_NAME" < backend/script/sql/update/aihr_20260817_knowledge_review_assistance_mysql8.sql