dsh-compaction-cacheaware: A Reasonix-Style Compaction Backend in DeepSeek Harness

`dsh-compaction-cacheaware` is a modular plugin designed for DeepSeek Harness (DSH), intended to replace the default compaction strategy with Reasonix-style cache-aware compaction. The plugin registers only the `ctx.compaction` interface, without interfering with other components, and supports automatic synchronization and Realm self-checks. Through a single trigger mechanism and a structured checkpoint design, it optimizes long-context processing. After installation, it must be manually configured in the Agent preset to replace `compaction-basic`, and requires Node.js >= 22.