fix(aihr): add semantic daily drill scoring fallback

backend/script/sql/update/aihr_20260714_daily_drill_score_mode_mysql8.sql

@@ -0,0 +1,23 @@
+-- 每日三题评分模式留痕：幂等补列，不写入业务数据。
+SET @db_name = DATABASE();
+SET @table_exists = (
+  SELECT COUNT(*)
+  FROM information_schema.tables
+  WHERE table_schema = @db_name
+    AND table_name = 'aihr_practice_assignment'
+);
+SET @column_exists = (
+  SELECT COUNT(*)
+  FROM information_schema.columns
+  WHERE table_schema = @db_name
+    AND table_name = 'aihr_practice_assignment'
+    AND column_name = 'score_mode'
+);
+SET @ddl = IF(
+  @table_exists = 1 AND @column_exists = 0,
+  'ALTER TABLE aihr_practice_assignment ADD COLUMN score_mode varchar(30) DEFAULT NULL COMMENT ''评分模式 LLM/RULE_FALLBACK'' AFTER score',
+  'SELECT 1'
+);
+PREPARE stmt FROM @ddl;
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;