1jincheng/dsh-first-paint

First-paint splash for DSH: pushes a branded splash page into the boot HTML as an index-injection row, so the desktop window opens already showing the splash instead of a white/loading flash. Fades out and hands over once the startup-animation plugin starts (checked via `window.__DSH_STARTUP_RUNNING__`), with a 6-second fallback (configurable via `maxMs`) so it can never trap the app behind the splash. A normal dsh.bundle plugin: no host changes, no app.asar patching.