Max-Null/dsh-capture

Dual-engine screen capture for DSH: inside the SSiD desktop shell, a global hotkey or tray opens a fullscreen box-select overlay (all monitors, per-display pixel-perfect frames) with in-place red-box annotation and a WeChat-style toolbar; in plain DSH (browser), the composer camera button captures the display via getDisplayMedia and reuses the same single-phase box-select + annotation overlay in-page. The cropped image lands in the current conversation composer through the official attachment intake.