dsh-idle-compactor: An Idle-Triggered Context Compression Plugin

The `dsh-idle-compactor` plugin adds a time- and state-based context compaction mechanism to DeepSeek Harness. It triggers compaction when a session has remained idle for an extended period and exceeds the token threshold, avoiding costs for stale context tails. The plugin supports configurable idle time, context size, and scan interval, and handles background tasks and archived sessions, effectively addressing context bloat in long conversations.