dsh-cron: Cron Expression Parsing and Execution Time Calculation

`dsh-cron` is a DeepSeek Harness plugin implemented in pure Node.js for parsing standard 5-field cron expressions. It not only returns a human-readable task description but also calculates the next and the following N execution times. After installation, configure `dsh.profile.bundles` in `package.json`. To use it, simply invoke the `cron_parse` tool. Because it involves running third-party code, users should review the source code themselves.