dsh-local-dba: Local Database Management Plugin

The DeepSeek Harness plugin `dsh-local-dba` provides a set of `db_*` tools that support querying, schema inspection, backup and recovery, and slow query analysis for MySQL/MariaDB and PostgreSQL. It is implemented in pure ESM JavaScript, requires no build step, and works out of the box. The plugin includes a UI for configuration, supports adding and removing connections, and defaults to read-only mode; write operations and backup/recovery are allowed only after enabling specific switches. It is recommended to manage passwords via environment variables when using the plugin and to ensure that the corresponding native database clients are installed on the system.