dsh-quicktime-player: Add a video player with draggable progress to the DSH sidebar

dsh-quicktime-player is a client-side DSH plugin maintained by rUrU516 that integrates video playback into the right sidebar: it registers its own tab type, ensuring that video playback from the file tab, chat references, or the file trees of other plugins all converges into the same player. The host routing uses HTTP Range requests to return status 206, allowing the progress bar to be dragged without loading entire large files into memory; on the desktop, it pulls streams from a 127.0.0.1 port with a token to bypass seek restrictions under dsh-app://. It supports zooming with the scroll wheel and panning at the pointer, frame-by-frame stepping, speed/cycle/volume control, remembering playback position by absolute path, as well as capturing frames to the clipboard and exporting clips using FFmpeg stream copy. The installation command is `dsh plugin --profile <profile> add dsh-quicktime-player`, which requires profile bundles; FFmpeg is only used for clip export, and if it is missing, the button will show a prompt. There are no configuration options; the core consists of a tab type and a single route.