feat: move remote desktop (RDP/VNC/Telnet) into a first-party plugin

Relocates guacamole backend/frontend source and tests into
plugins/remote-desktop, following the ssh-terminal/docker pattern.

plugins/remote-desktop/frontend/guacamole-zoom.ts

@@ -0,0 +1,11 @@
+export const MIN_GUACAMOLE_ZOOM = 0.5;
+export const MAX_GUACAMOLE_ZOOM = 4;
+export const GUACAMOLE_ZOOM_STEP = 0.25;
+
+export function clampGuacamoleZoom(zoom: number): number {
+  return Math.min(MAX_GUACAMOLE_ZOOM, Math.max(MIN_GUACAMOLE_ZOOM, zoom));
+}
+
+export function stepGuacamoleZoom(zoom: number, direction: -1 | 1): number {
+  return clampGuacamoleZoom(zoom + direction * GUACAMOLE_ZOOM_STEP);
+}