dsh-nexus: Zero-Config Memory Layer for DeepSeek Harness

`dsh-nexus` is a zero-configuration memory-layer plugin designed specifically for DeepSeek Harness (DSH), using an “atomic + gated + auditable” three-tier structure to manage memory. The plugin provides cost control, auditing, and data cleanup through a visual dashboard, with support for budget highlighting, automatic detection of erroneous writes, and three-stage deletion (archive → trash → permanent deletion). For security, it hardens against attacks via Origin validation and Host restrictions, and supports scanning for sensitive information. The plugin is not yet published to npm and must be installed from a GitHub source or a local tarball; it is currently in a “record-only, non-blocking” shadow phase.