dsh-when: Parsing Chinese Natural-Language Relative Time into ISO Timestamps

dsh-when is a zero-dependency ESM plugin for DeepSeek Harness (DSH) that parses natural-language time phrases (such as "tomorrow at 9:00" or "in 2 hours") into ISO 8601 timestamps. It mounts the `when` tool, supports day-offset, duration, weekday, clock-time, and ISO 8601 modes, and defaults to the local time zone. The plugin follows a fail-fast principle, parsing only explicitly supported phrases, and is commonly used alongside dsh-cron-parse and dsh-scheduler.