[Studio] feat: add MySQL persistence and the deployment it needs

[lizhimins]

Studio kept everything in memory, so topics, groups, settings, audit records
and query history were lost on restart.

• MyBatis-Plus + MySQL 8.0 with a single authoritative schema (9 tables) and
  sample data for an e-commerce trade flow
• entities, mappers and a MyBatis-Plus backed settings repository
• OperationAuditService records mutations, wired into settings and audit
• compose runs MySQL alongside the server, pinned to Asia/Shanghai with an
  explicit UTF-8 JDBC connection
• attach MySQL to the rocketmq network and drop the nginx runtime resolver:
  under podman the first DNS answers NXDOMAIN, which broke the datasource and
  caused sporadic 502s on /api