add admin dashboard for viewing DiffMT results

add admin endpoint to retrieve full session list for dashboard

enhance delete-session functionality to optionally keep trial clicks

add delete-session admin endpoint and manage_results command

add delete-user admin endpoint and manage_results command

fix admin auth for private HF Space; add manage_results script

add session management for trials; implement immediate saving and player name attachment

implement admin authentication for data export and reset endpoints; update game timing and add hint in HTML

refactor server.js to support configurable data file path and ensure directory structure on startup

add initial game implementation with HTML, CSS, and JavaScript