feat(课堂看板): 「这节课」那排题号后面写上几点布置的，之后改题不变

class_lesson 加 created_at（0034，老数据用 updated_at 回填），「改」只动 updated_at；
清掉再布置算重新开始。

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/api/src/db/meta/_journal.json

@@ -239,6 +239,13 @@
       "when": 1791823809856,
       "tag": "0033_drop_message",
       "breakpoints": true
+    },
+    {
+      "idx": 34,
+      "version": "7",
+      "when": 1791858070886,
+      "tag": "0034_add_class_lesson_created_at",
+      "breakpoints": true
     }
   ]
 }