feat: add database topic group with 105 questions

- mysql-acid (35): undo/redo log, WAL, 崩溃恢复三阶段, 两阶段提交
- mysql-transaction-isolation (35): 四隔离级别, 三异常, Read View, 快照读/当前读, next-key lock
- redis-persistence (35): RDB/AOF/混合持久化, AOF 重写, vs binlog/redo log
- 每子主题: single_choice×10 + fill_blank×10 + short_answer×10 + code_reading×5
- 全部通过 question.schema.json 校验

topics/database/redis-persistence/meta.json

@@ -0,0 +1,57 @@
+{
+  "slug": "redis-persistence",
+  "name": "Redis 持久化与日志对比",
+  "description": "AOF/RDB 持久化机制、AOF 重写压缩原理、与 MySQL binlog/redo log/undo log 的对比（数据结构角度）",
+  "tags": [
+    "AOF",
+    "AOF重写",
+    "InnoDB成",
+    "MySQL",
+    "PITR",
+    "RDB",
+    "Redis",
+    "WAL",
+    "appendfsync",
+    "binlog",
+    "innodb_flush",
+    "position",
+    "redo",
+    "redo log",
+    "不膨胀",
+    "压缩",
+    "同步配置对比",
+    "对应关系",
+    "对比",
+    "持久化",
+    "持久性",
+    "日志",
+    "日志对比",
+    "时间点恢复",
+    "状态快照",
+    "环形",
+    "综合",
+    "覆盖",
+    "选型"
+  ],
+  "difficulty_range": [
+    2,
+    4
+  ],
+  "schema_version": "1.0.0",
+  "updated": "2026-09-07",
+  "question_files": [
+    "single_choice",
+    "fill_blank",
+    "code_reading",
+    "short_answer"
+  ],
+  "stats": {
+    "total": 35,
+    "by_type": {
+      "single_choice": 10,
+      "fill_blank": 10,
+      "code_reading": 5,
+      "short_answer": 10
+    }
+  }
+}