dsh-heartbeat: Autonomous Heartbeat Plugin for DeepSeek Harness

`dsh-heartbeat` is a DeepSeek Harness (DSH) plugin that gives an Agent an autonomous "heartbeat" and a sense of presence. Every 20 minutes, it runs a seven-phase cycle that includes maintenance, collection, wandering, gating, rumination, and delivery. A discretion gate checks conditions such as quiet hours and user status to decide whether the Agent should speak, while a material pool and `web_search` support perception and accumulation. The plugin supports profile maintenance, ledger accounting, and local encrypted storage, and is Windows-only.