dsh-loop: DeepSeek Harness Scheduled Loop Plugin

The `dsh-loop` plugin for DeepSeek Harness (DSH) simplifies the scheduling logic for periodic agent tasks under the “everything is a plugin” design philosophy. It provides developers with a user-friendly `/loop` command that supports custom time intervals (including combined durations), as well as configuration persistence, status queries, and manual stopping. Developers can directly control an agent's looping behavior from the Web interface without writing complex code. After installation, restart the application; it is supported only in Profile environments that include a command adapter.