dsh-hash-edit: DeepSeek Harness Hash-Anchored Read/Write Plugin

`dsh-hash-edit` is a hash-anchoring plugin for DeepSeek Harness. It uses the xxHash32 algorithm to generate stable base-62 anchors for file lines, resolving positioning failures caused by line-number changes. The plugin takes over editing operations, rejects fuzzy matching, and supports persistent undo. Users should follow a single-edit discipline, performing deletions and replacements with pure three-character hashes. It supports files with up to 238,328 lines and a size of up to 100 MB.