feat(aihr): add SOP answer thumbs up/down feedback loop

- New aihr_knowledge_answer_feedback table; unique (tenant, query_norm,
  fragment_id) pair keeps submissions idempotent
- POST /api/knowledge/answer-feedback (fragmentIds array), GET pending-review
  list, POST /{id}/review — all under existing auth scope
- Down-voted (question, fragment) pairs are filtered from dbSearch fusion
  results; if filtering empties the hit list the original results are kept
  with an explanatory caution (never degrade to no-answer)
- Feedback table missing/unreachable → filter silently skipped, search
  behavior unchanged (degradation chain preserved)
- SnippetResponse gains optional trailing fragmentId (db hits only; seed
  fallback stays null); mobile sopPanel adds 👍/👎 with locked state after
  submit, up votes auto-marked reviewed to keep the review queue clean

backend/script/sql/aihr_practice_mysql8.sql

@@ -219,6 +219,25 @@ CREATE TABLE IF NOT EXISTS `aihr_sop_answer_review` (
   KEY `idx_aihr_sop_answer_review_status` (`tenant_id`, `status`, `create_time`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci COMMENT='AI HR SOP问答人工评审';
 
+CREATE TABLE IF NOT EXISTS `aihr_knowledge_answer_feedback` (
+  `id` bigint NOT NULL AUTO_INCREMENT COMMENT '主键',
+  `tenant_id` varchar(20) DEFAULT '000000' COMMENT '租户编号',
+  `query_text` varchar(1000) NOT NULL COMMENT '问题原文',
+  `query_norm` varchar(500) NOT NULL COMMENT '规范化问题',
+  `fragment_id` bigint NOT NULL COMMENT '知识片段ID',
+  `verdict` varchar(10) NOT NULL COMMENT '反馈: up/down',
+  `category` varchar(100) DEFAULT NULL COMMENT '知识分类',
+  `position` varchar(80) DEFAULT NULL COMMENT '岗位',
+  `source` varchar(50) DEFAULT 'knowledge_search' COMMENT '来源',
+  `review_status` varchar(30) DEFAULT '待复核' COMMENT '复核状态',
+  `create_time` datetime DEFAULT NULL COMMENT '创建时间',
+  `update_time` datetime DEFAULT NULL COMMENT '更新时间',
+  PRIMARY KEY (`id`),
+  UNIQUE KEY `uk_aihr_answer_feedback_pair` (`tenant_id`, `query_norm`, `fragment_id`),
+  KEY `idx_aihr_answer_feedback_verdict` (`tenant_id`, `query_norm`, `fragment_id`, `verdict`),
+  KEY `idx_aihr_answer_feedback_review` (`tenant_id`, `review_status`, `create_time`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci COMMENT='AI HR 知识答案反馈';
+
 INSERT INTO `aihr_practice_scenario`
   (`tenant_id`, `scenario_code`, `scenario_name`, `position`, `scenario_type`, `project_type`, `difficulty`,
    `customer_persona`, `opening_text`, `explicit_need`, `hidden_need`, `irritants`, `delights`, `sop_refs`,