AlLHHH/dsh-perf-boost

Performance optimization and smoothness enhancement for DSH Desktop (renderer-side only; host code untouched, no on-disk config): skips offscreen message rendering, stops frames and timers while the window is hidden, lazily loads media, coalesces session-list repaints and pre-warms large session files; shows the measured main-thread saving in settings. A lightweight speed-up for lag, dropped frames, slow large-session opening and background CPU use.