dsh-headwater: Give Harness Agent a "Memory of Its Own"

Introducing `dsh-headwater`, a DSH plugin maintained by h1-cat (Category: Memory). It does not load models or perform vector retrieval, but utilizes a three-layer file structure to separate original text from understanding: `episodes.jsonl` records every sentence verbatim, appended without rewriting; `book.json` records current understanding, a ledger of relationships, pending items, stances, and repeated statements. The plugin attaches memory to the end of the prompt for each round, providing `headwater_check` for five-level propriety judgment, `headwater_recall` to look up original text, `headwater_portrait` to rewrite understanding, automatic recalculation every 8 rounds, and sampling from original text to calibrate tone. The article provides official installation commands, configuration options, data locations, and applicable cautions.