dsh-sidebar-panel: Adding a persistent right-side panel to DSH Web

# Introduction In the DSH (DeepSeek Harness) web interface, there are several types of information that are not easily visible during normal use: context window usage, session costs, files in the workspace, and modified files in the session. Although the details column on the right carries some of this content, it is automatically collapsed when switching or creating new sessions, requiring manual reopening each time. The dsh-sidebar-panel approach is to add a panel collapse button in the top-right corner of the session header, place the Overview, Files, Changes, and Tools tabs into the right details column, and make the panel persistent—switching or creating new sessions does not automatically collapse it, and the collapsed state is also remembered. # What is it dsh-sidebar-panel is DSH We...