dsh-tool-everything: Integrate Everything full-disk file search for DSH Agent

`dsh-tool-everything` is an Everything search plugin for DSH (DeepSeek Harness) that registers the `everything_search` tool for an Agent. It directly invokes the local Everything NTFS index on Windows to perform millisecond-level full-disk searches by filename, without needing to enable an HTTP server or es.exe. The plugin loads the bundled Everything64.dll (taken from Everything SDK 1.5) via the koffi FFI, communicates with Everything through an IPC channel, and returns structured results (path, size, is a folder). It supports the full Everything search syntax, such as wildcards.