dsh-navigation-bar: Adding Piano Key-Style Multi-Level Navigation to DSH Web Sessions

`KeLearns/dsh-navigation-bar` is a client-side plugin designed for the DSH Web GUI, aimed at solving the difficulty of locating messages in long sessions. Developed based on the official DSH dual-panel plugin mechanism, it does not intrude on the source code and adheres to the MIT license. Its core function maps user messages in a session into a row of "piano key" navigation bars, where each key corresponds to a user message (including steering messages), and model responses are incorporated into the previews of corresponding rounds. The plugin offers a rich visual interaction experience: the navigation bar is vertically centered with fixed key spacing and height; on hover, keys elongate and display preview bubbles (single line for user messages, three lines with ellipsis for model responses), with adjacent keys above and below forming a stepped visual effect; the key corresponding to the currently viewed content highlights in real-time as scrolling occurs. It supports adaptive dark and light themes through the official DSH